feat: 完善AI生成頁面功能與體驗

- 修復詞彙顏色邏輯，實現基於用戶程度的相對難度顯示
- A2用戶看B2詞彙現在正確顯示橘色(挑戰等級)，而非固定藍色
- 新增分析結果localStorage持久化，跳頁後保留分析內容
- 添加簡潔的用戶程度指示器，使用經典齒輪圖標
- 程度按鈕靠右對齊，固定灰色主題，清楚導航到設定頁面

提升個人化學習體驗和界面一致性

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

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

frontend/app/generate/page.tsx

@@ -1,12 +1,12 @@
 'use client'
 
-import { useState, useMemo, useCallback } from 'react'
+import { useState, useMemo, useCallback, useEffect } from 'react'
 import { ProtectedRoute } from '@/components/shared/ProtectedRoute'
 import { Navigation } from '@/components/shared/Navigation'
 import { WordPopup } from '@/components/word/WordPopup'
 import { useToast } from '@/components/shared/Toast'
 import { flashcardsService } from '@/lib/services/flashcards'
-import { getLevelIndex, getTargetLearningRange } from '@/lib/utils/cefrUtils'
+import { getLevelIndex } from '@/lib/utils/cefrUtils'
 import { useWordAnalysis } from '@/hooks/word/useWordAnalysis'
 import { API_CONFIG } from '@/lib/config/api'
 import Link from 'next/link'
@@ -49,8 +49,50 @@ function GenerateContent() {
   const [selectedIdiom, setSelectedIdiom] = useState<string | null>(null)
   const [selectedWord, setSelectedWord] = useState<string | null>(null)
 
+  // localStorage 快取函數
+  const saveAnalysisToCache = useCallback((cacheData: any) => {
+    try {
+      localStorage.setItem('generate_analysis_cache', JSON.stringify(cacheData))
+    } catch (error) {
+      console.warn('無法保存分析快取:', error)
+    }
+  }, [])
+
+  const loadAnalysisFromCache = useCallback(() => {
+    try {
+      const cached = localStorage.getItem('generate_analysis_cache')
+      return cached ? JSON.parse(cached) : null
+    } catch (error) {
+      console.warn('無法載入分析快取:', error)
+      return null
+    }
+  }, [])
+
+  const clearAnalysisCache = useCallback(() => {
+    try {
+      localStorage.removeItem('generate_analysis_cache')
+    } catch (error) {
+      console.warn('無法清除分析快取:', error)
+    }
+  }, [])
+
+  // 組件載入時恢復快取的分析結果
+  useEffect(() => {
+    const cached = loadAnalysisFromCache()
+    if (cached) {
+      setTextInput(cached.textInput || '')
+      setSentenceAnalysis(cached.sentenceAnalysis || null)
+      setSentenceMeaning(cached.sentenceMeaning || '')
+      setGrammarCorrection(cached.grammarCorrection || null)
+      setShowAnalysisView(cached.showAnalysisView || false)
+      console.log('✅ 已恢復快取的分析結果')
+    }
+  }, [loadAnalysisFromCache])
+
   // 處理句子分析 - 使用真實API
   const handleAnalyzeSentence = async () => {
+    // 清除舊的分析快取
+    clearAnalysisCache()
 
     setIsAnalyzing(true)
 
@@ -126,6 +168,29 @@ function GenerateContent() {
       }
 
       setShowAnalysisView(true)
+
+      // 保存分析結果到快取
+      const cacheData = {
+        textInput,
+        sentenceAnalysis: analysisData,
+        sentenceMeaning: apiData.sentenceMeaning || '',
+        grammarCorrection: apiData.grammarCorrection ? {
+          hasErrors: apiData.grammarCorrection.hasErrors,
+          originalText: textInput,
+          correctedText: apiData.grammarCorrection.correctedText || textInput,
+          corrections: apiData.grammarCorrection.corrections || [],
+          confidenceScore: apiData.grammarCorrection.confidenceScore || 1.0
+        } : {
+          hasErrors: false,
+          originalText: textInput,
+          correctedText: textInput,
+          corrections: [],
+          confidenceScore: 1.0
+        },
+        showAnalysisView: true
+      }
+      saveAnalysisToCache(cacheData)
+
     } catch (error) {
       console.error('Error in sentence analysis:', error)
       setGrammarCorrection({
@@ -299,32 +364,25 @@ function GenerateContent() {
                   '🔍 分析句子'
                 )}
               </button>
-
-
-              {/* 個人化程度指示器 */}
-              <div className="text-center text-sm text-gray-600 mt-2">
-                {(() => {
-                  const userLevel = localStorage.getItem('userEnglishLevel') || 'A2'
-                  return (
-                    <div className="flex items-center justify-center gap-2">
-                      <span>🎯 您的程度: {userLevel}</span>
-                      <span className="text-gray-400">|</span>
-                      <span>📈 重點學習範圍: {getTargetLearningRange(userLevel)}</span>
-                      <Link
-                        href="/settings"
-                        className="text-blue-500 hover:text-blue-700 ml-2"
-                      >
-                        調整 ⚙️
-                      </Link>
-                    </div>
-                  )
-                })()}
-              </div>
             </div>
           </>
         ) : (
           /* 重新設計的句子分析視圖 - 簡潔流暢 */
           <>
+            {/* 用戶程度指示器 */}
+            <div className="flex justify-end mb-6">
+              <Link
+                href="/profile"
+                className="flex items-center gap-2 px-4 py-2 rounded-lg transition-colors hover:shadow-md bg-gray-100 text-gray-700 border border-gray-200"
+              >
+                <span className="text-sm font-medium">你的程度 {userLevel}</span>
+                  <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24" strokeWidth="2">
+                    <path d="M12 15a3 3 0 100-6 3 3 0 000 6z"/>
+                    <path d="M19.4 15a1.65 1.65 0 00.33 1.82l.06.06a2 2 0 010 2.83 2 2 0 01-2.83 0l-.06-.06a1.65 1.65 0 00-1.82-.33 1.65 1.65 0 00-1 1.51V21a2 2 0 01-2 2 2 2 0 01-2-2v-.09A1.65 1.65 0 009 19.4a1.65 1.65 0 00-1.82.33l-.06.06a2 2 0 01-2.83 0 2 2 0 010-2.83l.06-.06a1.65 1.65 0 00.33-1.82 1.65 1.65 0 00-1.51-1H3a2 2 0 01-2-2 2 2 0 012-2h.09A1.65 1.65 0 004.6 9a1.65 1.65 0 00-.33-1.82l-.06-.06a2 2 0 010-2.83 2 2 0 012.83 0l.06.06a1.65 1.65 0 001.82.33H9a1.65 1.65 0 001-1.51V3a2 2 0 012-2 2 2 0 012 2v.09a1.65 1.65 0 001 1.51 1.65 1.65 0 001.82-.33l.06-.06a2 2 0 012.83 0 2 2 0 010 2.83l-.06.06a1.65 1.65 0 00-.33 1.82V9a1.65 1.65 0 001.51 1H21a2 2 0 012 2 2 2 0 01-2 2h-.09a1.65 1.65 0 00-1.51 1z"/>
+                  </svg>
+              </Link>
+            </div>
+
             {/* 語法修正面板 - 如果需要的話 */}
             {grammarCorrection && grammarCorrection.hasErrors && (
               <div className="bg-yellow-50 border border-yellow-200 rounded-xl p-6 mb-6">