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_en.arb

@@ -487,5 +487,23 @@
   "settingsDoNotSellTitle": "Personalized Ads",
   "settingsDoNotSellDescription": "When off, your personal info won't be used for ad recommendations",
   "settingsDoNotSellEnabled": "Off",
-  "settingsDoNotSellDisabled": "On"
+  "settingsDoNotSellDisabled": "On",
+  "settingsFeedbackTitle": "Feedback",
+  "feedbackTitle": "Feedback",
+  "feedbackTypeLabel": "Feedback Type",
+  "feedbackTypeBug": "Bug",
+  "feedbackTypeSuggestion": "Suggestion",
+  "feedbackTypeOther": "Other",
+  "feedbackContentLabel": "Content",
+  "feedbackContentHint": "Please describe your issue or suggestion in detail...",
+  "feedbackImagesLabel": "Add Screenshots (max 3)",
+  "feedbackAnonymousLabel": "Do not upload my personal information",
+  "feedbackAnonymousHint": "If checked, your user ID will not be collected. Device info will still be collected for troubleshooting.",
+  "feedbackSubmit": "Submit Feedback",
+  "feedbackSubmitting": "Submitting...",
+  "feedbackSuccess": "Thank you for your feedback. We will process it soon.",
+  "feedbackContentRequired": "Please enter feedback content",
+  "feedbackContentTooLong": "Feedback content cannot exceed 500 characters",
+  "feedbackTooManyImages": "Maximum 3 images allowed",
+  "feedbackImageTooLarge": "Image size cannot exceed 5MB"
 }