feat(feedback): implement user feedback collection system with email reporting

Backend:
- Add user_feedback table with RLS policy
- Create feedback submission API (multipart/form-data)
- Implement xlsx report generation with embedded images
- Add scheduled email delivery via Feishu SMTP
- Create HTML email templates (daily_report, no_feedback)

Frontend:
- Add feedback screen with type selection and image picker
- Support anonymous submission via skipAuth flag
- Collect device info and app version

Protocol:
- Document feedback API contract and error codes
- Update http-error-codes.md with FEEDBACK_* codes

apps/lib/l10n/app_zh_hant.arb

@@ -389,5 +389,23 @@
   "settingsDoNotSellTitle": "個人化廣告推薦",
   "settingsDoNotSellDescription": "關閉後，我們不會將您的個人資訊用於廣告推薦",
   "settingsDoNotSellEnabled": "已關閉",
-  "settingsDoNotSellDisabled": "已開啟"
+  "settingsDoNotSellDisabled": "已開啟",
+  "settingsFeedbackTitle": "意見回饋",
+  "feedbackTitle": "意見回饋",
+  "feedbackTypeLabel": "回饋類型",
+  "feedbackTypeBug": "問題回饋",
+  "feedbackTypeSuggestion": "功能建議",
+  "feedbackTypeOther": "其他",
+  "feedbackContentLabel": "回饋內容",
+  "feedbackContentHint": "請詳細描述您的問題或建議...",
+  "feedbackImagesLabel": "添加截圖（最多3張）",
+  "feedbackAnonymousLabel": "不上傳我的個人信息",
+  "feedbackAnonymousHint": "勾選後將不採集您的用戶ID，僅採集設備信息用於問題排查",
+  "feedbackSubmit": "提交回饋",
+  "feedbackSubmitting": "提交中...",
+  "feedbackSuccess": "感謝您的回饋，我們會盡快處理",
+  "feedbackContentRequired": "請輸入回饋內容",
+  "feedbackContentTooLong": "回饋內容不能超過500字",
+  "feedbackTooManyImages": "最多只能上傳3張圖片",
+  "feedbackImageTooLarge": "圖片大小不能超過5MB"
 }