fix: 修正手機端詞彙popup定位問題

- 解決手機版popup容易被屏幕邊緣截掉的問題
- 實現響應式popup寬度：min(320px, calc(100vw - 32px))
- 針對手機端(≤640px)特殊處理：popup自動居中顯示
- 優化邊界檢測邏輯，確保popup始終在可視範圍內
- 大屏幕保持智能定位，小屏幕採用安全居中策略
- 添加動態寬度計算，適應不同屏幕尺寸
- 預留最小邊距16px，避免popup貼邊顯示

修正後手機端用戶體驗大幅改善，popup不再被截掉。

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

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

frontend/components/ClickableTextV2.tsx

@@ -75,17 +75,40 @@ export function ClickableTextV2({
     const wordAnalysis = analysis?.[cleanWord]
 
     const rect = event.currentTarget.getBoundingClientRect()
+    const viewportWidth = window.innerWidth
     const viewportHeight = window.innerHeight
+    const popupWidth = 320 // popup寬度 w-80 = 320px
     const popupHeight = 400 // 估計popup高度
 
-    // 智能定位：如果上方空間不足，就顯示在下方
+    // 智能水平定位，適應不同屏幕尺寸
+    let x = rect.left + rect.width / 2
+    const actualPopupWidth = Math.min(popupWidth, viewportWidth - 32) // 實際popup寬度
+    const halfPopupWidth = actualPopupWidth / 2
+    const padding = 16 // 最小邊距
+
+    // 手機端特殊處理
+    if (viewportWidth <= 640) { // sm斷點
+      // 小屏幕時居中顯示，避免邊緣問題
+      x = viewportWidth / 2
+    } else {
+      // 大屏幕時智能調整位置
+      if (x + halfPopupWidth + padding > viewportWidth) {
+        x = viewportWidth - halfPopupWidth - padding
+      }
+      if (x - halfPopupWidth < padding) {
+        x = halfPopupWidth + padding
+      }
+    }
+
+    // 計算垂直位置
     const spaceAbove = rect.top
     const spaceBelow = viewportHeight - rect.bottom
+    const showBelow = spaceAbove < popupHeight
 
     const position = {
-      x: rect.left + rect.width / 2,
+      x: x,
-      y: spaceAbove >= popupHeight ? rect.top - 10 : rect.bottom + 10,
+      y: showBelow ? rect.bottom + 10 : rect.top - 10,
-      showBelow: spaceAbove < popupHeight
+      showBelow: showBelow
     }
 
     if (wordAnalysis) {
@@ -287,13 +310,14 @@ export function ClickableTextV2({
       {/* 現代風格詞彙彈窗 */}
       {selectedWord && analysis?.[selectedWord] && (
         <div
-          className="fixed z-50 bg-white rounded-2xl shadow-2xl border-0 w-80 backdrop-blur-sm"
+          className="fixed z-50 bg-white rounded-2xl shadow-2xl border-0 backdrop-blur-sm"
           style={{
             left: `${popupPosition.x}px`,
             top: `${popupPosition.y}px`,
             transform: popupPosition.showBelow
               ? 'translate(-50%, 8px)'
               : 'translate(-50%, calc(-100% - 8px))',
+            width: 'min(320px, calc(100vw - 32px))', // 響應式寬度，手機端自動收縮
             maxHeight: '85vh',
             overflowY: 'auto',
             background: 'rgba(255, 255, 255, 0.98)',