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/presentation/screens/settings_screen.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 
+import '../../../../data/network/api_client.dart';
 import '../../../../l10n/app_localizations.dart';
 import '../../../../shared/theme/design_tokens.dart';
 import '../../../../shared/widgets/app_modal_dialog.dart';
@@ -9,6 +10,7 @@ import '../../data/repositories/invite_repository.dart';
 import 'account_delete_screen.dart';
 import '../widgets/settings_section_widgets.dart';
 import 'coin_center_screen.dart';
+import 'feedback_screen.dart';
 import 'general_settings_screen.dart';
 import 'invite_screen.dart';
 import 'legal_center_screen.dart';
@@ -21,6 +23,7 @@ class SettingsScreen extends StatefulWidget {
     required this.settings,
     required this.coinBalance,
     required this.inviteRepository,
+    required this.apiClient,
     required this.onInterfaceLanguageChanged,
     required this.onSettingsChanged,
     required this.onUploadAvatar,
@@ -33,6 +36,7 @@ class SettingsScreen extends StatefulWidget {
   final ProfileSettingsV1 settings;
   final int coinBalance;
   final InviteRepository inviteRepository;
+  final ApiClient apiClient;
   final Future<void> Function(String languageTag) onInterfaceLanguageChanged;
   final Future<void> Function(ProfileSettingsV1 settings) onSettingsChanged;
   final Future<ProfileSettingsV1> Function(String filePath) onUploadAvatar;
@@ -125,6 +129,23 @@ class _SettingsScreenState extends State<SettingsScreen> {
               ),
             ],
           ),
+          const SizedBox(height: AppSpacing.xl),
+          SettingsGroupCard(
+            children: [
+              SettingsMenuTile(
+                icon: Icons.feedback_outlined,
+                title: l10n.settingsFeedbackTitle,
+                tint: colors.primary,
+                background: colors.surfaceContainerHighest,
+                showDivider: false,
+                onTap: () => Navigator.of(context).push<void>(
+                  MaterialPageRoute<void>(
+                    builder: (_) => FeedbackScreen(apiClient: widget.apiClient),
+                  ),
+                ),
+              ),
+            ],
+          ),
           SettingsGroupCard(
             children: [
               SettingsMenuTile(