feat: 添加 OCR 词汇提取功能

新增 OCR 页面，用户可上传教材词汇表截图，使用 GLM-4.6V 视觉模型
提取单词-释义对并保存到指定文件夹。

- AI 管道: src/lib/bigmodel/ocr/ (orchestrator, types)
- 后端模块: src/modules/ocr/ (action-service-repository 架构)
- 前端页面: src/app/(features)/ocr/ (拖拽上传、folder 选择)
- i18n: 8 种语言翻译支持

messages/en-US.json

@@ -197,6 +197,35 @@
     "favorites": "Favorites",
     "settings": "Settings"
   },
+  "ocr": {
+    "title": "OCR Vocabulary Extractor",
+    "description": "Upload vocabulary table screenshots from textbooks to extract word-definition pairs",
+    "uploadImage": "Upload Image",
+    "dragDropHint": "Drag and drop an image here, or click to select",
+    "supportedFormats": "Supports: JPG, PNG, WebP",
+    "selectFolder": "Select Folder",
+    "chooseFolder": "Choose a folder to save extracted pairs",
+    "noFolders": "No folders available. Please create a folder first.",
+    "languageHints": "Language Hints (Optional)",
+    "sourceLanguageHint": "Source language (e.g., English)",
+    "targetLanguageHint": "Target/Translation language (e.g., Chinese)",
+    "process": "Process Image",
+    "processing": "Processing...",
+    "preview": "Preview",
+    "extractedPairs": "Extracted Pairs",
+    "word": "Word",
+    "definition": "Definition",
+    "pairsCount": "{count} pairs extracted",
+    "savePairs": "Save to Folder",
+    "saving": "Saving...",
+    "saved": "Successfully saved {count} pairs to {folder}",
+    "saveFailed": "Failed to save pairs",
+    "noImage": "Please upload an image first",
+    "noFolder": "Please select a folder",
+    "processingFailed": "OCR processing failed",
+    "tryAgain": "Please try again with a clearer image",
+    "detectedLanguages": "Detected: {source} → {target}"
+  },
   "profile": {
     "myProfile": "My Profile",
     "email": "Email: {email}",