feat: 實現慣用語彈窗智能定位 + 簡化 WordPopup 組件

## 慣用語彈窗智能定位系統
- ✅ 創建智能定位工具 (popupPositioning.ts)
- ✅ 自動檢測可用空間，防止彈窗被底部遮蔽
- ✅ 智能選擇彈出方向 (上方/下方/居中)
- ✅ 響應式適配：桌面智能定位 + 手機底部modal
- ✅ 修正底部慣用語點擊體驗問題

## WordPopup 組件簡化
- 🔧 移除未使用的 useState import
- 🔧 簡化過度的響應式設計 (移除多處 sm: 斷點)
- 🔧 替換 ContentBlock 為簡單 div 結構
- 🔧 簡化條件渲染邏輯 (IIFE → 簡單 &&)
- ✅ 統一字體大小，與慣用語彈窗保持一致

## 技術改進
- 📱 設備檢測：自動適配移動/桌面體驗
- 🎯 智能定位：邊界檢測 + 動態位置計算
- 🧹 代碼簡化：減少複雜度，提升維護性
- 🎨 設計統一：兩種彈窗風格對齊

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/app/generate/page.tsx

@@ -9,6 +9,7 @@ import { flashcardsService } from '@/lib/services/flashcards'
 import { compareCEFRLevels, getLevelIndex, getTargetLearningRange } from '@/lib/utils/cefrUtils'
 import { BluePlayButton } from '@/components/shared/BluePlayButton'
 import { API_CONFIG } from '@/lib/config/api'
+import { calculateSmartPopupPosition, isMobileDevice, getElementPosition } from '@/lib/utils/popupPositioning'
 import Link from 'next/link'
 
 // 常數定義
@@ -34,6 +35,7 @@ interface IdiomPopup {
   idiom: string;
   analysis: any;
   position: { x: number; y: number };
+  placement?: 'top' | 'bottom' | 'center';
 }
 
 function GenerateContent() {
@@ -442,15 +444,36 @@ function GenerateContent() {
                             key={index}
                             className="cursor-pointer transition-all duration-200 rounded-lg relative mx-0.5 px-1 py-0.5 inline-flex items-center gap-1 bg-blue-50 border border-blue-200 hover:bg-blue-100 hover:shadow-lg transform hover:-translate-y-0.5 text-blue-700 font-medium"
                             onClick={(e) => {
-                              // 使用新的API格式，直接使用idiom物件
+                              // 檢測移動設備
-                              setIdiomPopup({
+                              const isMobile = isMobileDevice()
-                                idiom: idiom.idiom,
+
-                                analysis: idiom,
+                              if (isMobile) {
-                                position: {
+                                // 移動設備：使用底部居中 modal
-                                  x: e.currentTarget.getBoundingClientRect().left + e.currentTarget.getBoundingClientRect().width / 2,
+                                setIdiomPopup({
-                                  y: e.currentTarget.getBoundingClientRect().bottom + 10
+                                  idiom: idiom.idiom,
-                                }
+                                  analysis: idiom,
-                              })
+                                  position: { x: 0, y: 0 }, // 移動版不使用計算位置
+                                  placement: 'center'
+                                })
+                              } else {
+                                // 桌面設備：使用智能定位系統
+                                const elementPosition = getElementPosition(e.currentTarget)
+                                const smartPosition = calculateSmartPopupPosition(
+                                  elementPosition,
+                                  384, // w-96 = 384px
+                                  400  // 預估高度
+                                )
+
+                                setIdiomPopup({
+                                  idiom: idiom.idiom,
+                                  analysis: idiom,
+                                  position: {
+                                    x: smartPosition.x,
+                                    y: smartPosition.y
+                                  },
+                                  placement: smartPosition.placement
+                                })
+                              }
                             }}
                             title={`${idiom.idiom}: ${idiom.translation}`}
                           >
@@ -494,7 +517,7 @@ function GenerateContent() {
           </div>
         )}
 
-        {/* 片語彈窗 */}
+        {/* 片語彈窗 - 智能定位系統 */}
         {idiomPopup && (
           <>
             <div
@@ -502,14 +525,27 @@ function GenerateContent() {
               onClick={() => setIdiomPopup(null)}
             />
             <div
-              className="fixed z-50 bg-white rounded-xl shadow-lg w-96 max-w-md overflow-hidden"
+              className={`
-              style={{
+                fixed z-50 bg-white rounded-xl shadow-lg overflow-hidden
-                left: `${idiomPopup.position.x}px`,
+                ${idiomPopup.placement === 'center' || isMobileDevice()
-                top: `${idiomPopup.position.y}px`,
+                  ? 'w-full max-w-md mx-4 top-1/2 left-1/2 transform -translate-x-1/2 -translate-y-1/2'
-                transform: 'translate(-50%, 8px)',
+                  : 'w-96 max-w-md'
-                maxHeight: '85vh',
+                }
-                overflowY: 'auto'
+              `}
-              }}
+              style={
+                idiomPopup.placement !== 'center' && !isMobileDevice()
+                  ? {
+                      left: `${idiomPopup.position.x}px`,
+                      top: `${idiomPopup.position.y}px`,
+                      transform: 'translate(-50%, 0)',
+                      maxHeight: '85vh',
+                      overflowY: 'auto'
+                    }
+                  : {
+                      maxHeight: '85vh',
+                      overflowY: 'auto'
+                    }
+              }
             >
               <div className="bg-gradient-to-br from-blue-50 to-indigo-50 p-5 border-b border-blue-200">
                 <div className="flex justify-end mb-3">

frontend/components/word/WordPopup.tsx

@@ -1,6 +1,5 @@
-import React, { useState } from 'react'
+import React from 'react'
 import { Modal } from '@/components/ui/Modal'
-import { ContentBlock } from '@/components/shared/ContentBlock'
 import { getCEFRColor } from '@/lib/utils/flashcardUtils'
 import { BluePlayButton } from '@/components/shared/BluePlayButton'
 import { useWordAnalysis } from '@/hooks/word/useWordAnalysis'
@@ -39,20 +38,18 @@ export const WordPopup: React.FC<WordPopupProps> = ({
   return (
     <Modal isOpen={isOpen} onClose={onClose} size="md">
       {/* Header */}
-      <div className="bg-gradient-to-br from-blue-50 to-indigo-50 p-4 sm:p-5 border-b border-blue-200">
+      <div className="bg-gradient-to-br from-blue-50 to-indigo-50 p-5 border-b border-blue-200">
         <div className="mb-3">
-          <h3 className="text-xl sm:text-2xl font-bold text-gray-900 break-words">
+          <h3 className="text-2xl font-bold text-gray-900">{getWordProperty(wordAnalysis, 'word')}</h3>
-            {getWordProperty(wordAnalysis, 'word')}
-          </h3>
         </div>
 
         <div className="flex items-center justify-between">
-          <div className="flex flex-col sm:flex-row sm:items-center gap-2 sm:gap-3">
+          <div className="flex items-center gap-3">
-            <span className="text-xs sm:text-sm bg-gray-100 text-gray-700 px-2 sm:px-3 py-1 rounded-full w-fit">
+            <span className="text-sm bg-gray-100 text-gray-700 px-3 py-1 rounded-full">
               {getWordProperty(wordAnalysis, 'partOfSpeech')}
             </span>
             <div className="flex items-center gap-2">
-              <span className="text-sm sm:text-base text-gray-600 break-all">
+              <span className="text-base text-gray-600">
                 {getWordProperty(wordAnalysis, 'pronunciation')}
               </span>
               <BluePlayButton
@@ -71,44 +68,42 @@ export const WordPopup: React.FC<WordPopupProps> = ({
       </div>
 
       {/* Content */}
-      <div className="p-3 sm:p-4 space-y-3 sm:space-y-4 max-h-96 overflow-y-auto">
+      <div className="p-4 space-y-4 max-h-96 overflow-y-auto">
         {/* Translation */}
-        <ContentBlock title="中文翻譯" variant="green">
+        <div className="bg-green-50 rounded-lg p-3 border border-green-200">
+          <h4 className="font-semibold text-green-900 mb-2 text-left text-sm">中文翻譯</h4>
           <p className="text-green-800 font-medium text-left">
             {getWordProperty(wordAnalysis, 'translation')}
           </p>
-        </ContentBlock>
+        </div>
 
         {/* Definition */}
-        <ContentBlock title="英文定義" variant="gray">
+        <div className="bg-gray-50 rounded-lg p-3 border border-gray-200">
-          <p className="text-gray-700 text-left text-sm leading-relaxed">
+          <h4 className="font-semibold text-gray-900 mb-2 text-left text-sm">英文定義</h4>
+          <p className="text-gray-700 text-left leading-relaxed">
             {getWordProperty(wordAnalysis, 'definition')}
           </p>
-        </ContentBlock>
+        </div>
 
         {/* Example */}
-        {(() => {
+        {getWordProperty(wordAnalysis, 'example') && (
-          const example = getWordProperty(wordAnalysis, 'example')
+          <div className="bg-blue-50 rounded-lg p-3 border border-blue-200">
-          return example && example !== 'null' && example !== 'undefined'
+            <h4 className="font-semibold text-blue-900 mb-2 text-left text-sm">例句</h4>
-        })() && (
-          <ContentBlock title="例句" variant="blue">
             <div className="space-y-2">
-              <p className="text-blue-800 text-left text-sm italic">
+              <p className="text-blue-800 text-left italic">
                 "{getWordProperty(wordAnalysis, 'example')}"
               </p>
-              <p className="text-blue-700 text-left text-sm">
+              <p className="text-blue-700 text-left">
                 {getWordProperty(wordAnalysis, 'exampleTranslation')}
               </p>
             </div>
-          </ContentBlock>
+          </div>
         )}
 
         {/* Synonyms */}
-        {(() => {
+        {getWordProperty(wordAnalysis, 'synonyms')?.length > 0 && (
-          const synonyms = getWordProperty(wordAnalysis, 'synonyms')
+          <div className="bg-purple-50 rounded-lg p-3 border border-purple-200">
-          return synonyms && Array.isArray(synonyms) && synonyms.length > 0
+            <h4 className="font-semibold text-purple-900 mb-2 text-left text-sm">同義詞</h4>
-        })() && (
-          <ContentBlock title="同義詞" variant="purple">
             <div className="flex flex-wrap gap-2">
               {getWordProperty(wordAnalysis, 'synonyms')?.map((synonym: string, index: number) => (
                 <span
@@ -119,13 +114,13 @@ export const WordPopup: React.FC<WordPopupProps> = ({
                 </span>
               ))}
             </div>
-          </ContentBlock>
+          </div>
         )}
       </div>
 
       {/* Save Button */}
       {onSaveWord && (
-        <div className="p-3 sm:p-4 pt-2">
+        <div className="p-4 pt-2">
           <button
             onClick={handleSaveWord}
             disabled={isSaving}

frontend/lib/utils/popupPositioning.ts

@@ -0,0 +1,139 @@
+/**
+ * 智能 Popup 定位工具
+ * 自動檢測可用空間，確保 popup 始終完全可見
+ */
+
+export interface PopupPosition {
+  x: number
+  y: number
+  placement: 'top' | 'bottom' | 'center'
+}
+
+export interface ClickPosition {
+  x: number
+  y: number
+  width: number
+  height: number
+}
+
+const POPUP_MARGIN = 16 // 與視窗邊緣的最小距離
+const POPUP_ARROW_OFFSET = 10 // 箭頭偏移量
+
+/**
+ * 計算智能 popup 位置
+ * @param clickRect 點擊元素的位置信息
+ * @param popupWidth popup 寬度 (預設 384px = w-96)
+ * @param popupHeight popup 高度 (預計值)
+ * @returns 計算後的最佳位置
+ */
+export function calculateSmartPopupPosition(
+  clickRect: ClickPosition,
+  popupWidth: number = 384,
+  popupHeight: number = 400
+): PopupPosition {
+  const viewportWidth = window.innerWidth
+  const viewportHeight = window.innerHeight
+  const scrollY = window.scrollY
+
+  // 計算點擊元素的中心點
+  const clickCenterX = clickRect.x + clickRect.width / 2
+  const clickCenterY = clickRect.y + clickRect.height / 2 + scrollY
+
+  // 檢測各方向可用空間
+  const spaceAbove = clickRect.y - POPUP_MARGIN
+  const spaceBelow = viewportHeight - (clickRect.y + clickRect.height) - POPUP_MARGIN
+  const spaceLeft = clickRect.x - POPUP_MARGIN
+  const spaceRight = viewportWidth - (clickRect.x + clickRect.width) - POPUP_MARGIN
+
+  // 判斷最佳垂直位置
+  let placement: 'top' | 'bottom' | 'center' = 'bottom'
+  let y: number
+
+  if (spaceBelow >= popupHeight) {
+    // 底部有足夠空間
+    placement = 'bottom'
+    y = clickRect.y + clickRect.height + POPUP_ARROW_OFFSET + scrollY
+  } else if (spaceAbove >= popupHeight) {
+    // 頂部有足夠空間
+    placement = 'top'
+    y = clickRect.y - popupHeight - POPUP_ARROW_OFFSET + scrollY
+  } else {
+    // 兩邊都沒有足夠空間，使用居中模式
+    placement = 'center'
+    y = Math.max(
+      POPUP_MARGIN + scrollY,
+      Math.min(
+        viewportHeight - popupHeight - POPUP_MARGIN + scrollY,
+        clickCenterY - popupHeight / 2
+      )
+    )
+  }
+
+  // 計算水平位置 (始終嘗試居中對齊點擊元素)
+  let x = clickCenterX - popupWidth / 2
+
+  // 確保不超出視窗邊界
+  x = Math.max(POPUP_MARGIN, Math.min(x, viewportWidth - popupWidth - POPUP_MARGIN))
+
+  return { x, y, placement }
+}
+
+/**
+ * 檢測是否為移動設備
+ * 移動設備使用底部 modal，桌面使用智能定位
+ */
+export function isMobileDevice(): boolean {
+  if (typeof window === 'undefined') return false
+  return window.innerWidth <= 768
+}
+
+/**
+ * 獲取元素的位置信息
+ * @param element DOM 元素
+ * @returns 位置信息
+ */
+export function getElementPosition(element: HTMLElement): ClickPosition {
+  const rect = element.getBoundingClientRect()
+  return {
+    x: rect.left,
+    y: rect.top,
+    width: rect.width,
+    height: rect.height
+  }
+}
+
+/**
+ * 創建平滑滾動效果，確保 popup 可見
+ * @param targetY popup 的 Y 位置
+ * @param popupHeight popup 高度
+ */
+export function ensurePopupVisible(targetY: number, popupHeight: number): void {
+  const viewportHeight = window.innerHeight
+  const scrollY = window.scrollY
+
+  // 計算 popup 的頂部和底部位置（相對於視窗）
+  const popupTop = targetY - scrollY
+  const popupBottom = popupTop + popupHeight
+
+  let needsScroll = false
+  let scrollTarget = scrollY
+
+  // 如果 popup 頂部被遮蔽
+  if (popupTop < POPUP_MARGIN) {
+    scrollTarget = targetY - POPUP_MARGIN
+    needsScroll = true
+  }
+  // 如果 popup 底部被遮蔽
+  else if (popupBottom > viewportHeight - POPUP_MARGIN) {
+    scrollTarget = targetY + popupHeight - viewportHeight + POPUP_MARGIN
+    needsScroll = true
+  }
+
+  // 執行平滑滾動
+  if (needsScroll) {
+    window.scrollTo({
+      top: scrollTarget,
+      behavior: 'smooth'
+    })
+  }
+}