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/features/settings/data/models/feedback.dart

@@ -0,0 +1,8 @@
+enum FeedbackType { bug, suggestion, other }
+
+class DeviceInfo {
+  const DeviceInfo({required this.platform, required this.model});
+
+  final String platform;
+  final String model;
+}