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/data/network/api_client.dart

@@ -20,6 +20,10 @@ class ApiClient {
       _dio.interceptors.add(
         InterceptorsWrapper(
           onRequest: (options, handler) async {
+            if (options.extra['skipAuth'] == true) {
+              handler.next(options);
+              return;
+            }
             final token = await tokenProvider();
             if (token != null && token.isNotEmpty) {
               options.headers['Authorization'] = 'Bearer $token';