feat: sync device timezone to backend on startup

On shell mount, reads the IANA timezone from the device via
flutter_timezone and POSTs it to PUT /api/settings as user_timezone.
Mirrors the web app's App.vue behaviour so briefing events and the
chat route use the correct local time on Android.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/app.dart

@@ -2,6 +2,8 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
+import 'package:flutter_timezone/flutter_timezone.dart';
+
 import 'core/constants.dart';
 import 'core/exceptions.dart';
 import 'core/theme.dart';
@@ -159,19 +161,29 @@ class _ShellState extends ConsumerState<_Shell> {
   @override
   void initState() {
     super.initState();
-    // Silent update check — only if we haven't already checked this session.
-    // Skipping when status is not idle/error prevents the dialog from
-    // re-appearing every time the shell re-mounts (e.g. after visiting settings).
     WidgetsBinding.instance.addPostFrameCallback((_) {
+      // Silent update check — only if we haven't already checked this session.
       final repoUrl = ref.read(forgejoRepoUrlProvider);
-      if (repoUrl == null || repoUrl.isEmpty) return;
-      final status = ref.read(updateProvider).status;
-      if (status == UpdateStatus.idle || status == UpdateStatus.error) {
-        ref.read(updateProvider.notifier).check(repoUrl);
+      if (repoUrl != null && repoUrl.isNotEmpty) {
+        final status = ref.read(updateProvider).status;
+        if (status == UpdateStatus.idle || status == UpdateStatus.error) {
+          ref.read(updateProvider.notifier).check(repoUrl);
+        }
       }
+      // Sync device timezone to backend so briefing and chat use local time.
+      _syncTimezone();
     });
   }
 
+  Future<void> _syncTimezone() async {
+    try {
+      final tzInfo = await FlutterTimezone.getLocalTimezone();
+      await ref.read(settingsApiProvider).syncTimezone(tzInfo.identifier);
+    } catch (_) {
+      // Best-effort — failure is non-critical.
+    }
+  }
+
   int _tabIndex(String location) {
     for (var i = 0; i < _tabs.length; i++) {
       if (location.startsWith(_tabs[i])) return i;

lib/data/api/settings_api.dart

@@ -0,0 +1,13 @@
+import 'package:dio/dio.dart';
+
+class SettingsApi {
+  const SettingsApi(this._dio);
+  final Dio _dio;
+
+  Future<void> syncTimezone(String ianaTimezone) async {
+    await _dio.put<void>(
+      '/api/settings',
+      data: {'user_timezone': ianaTimezone},
+    );
+  }
+}

lib/providers/api_client_provider.dart

@@ -10,6 +10,7 @@ import '../data/api/milestones_api.dart';
 import '../data/api/notes_api.dart';
 import '../data/api/projects_api.dart';
 import '../data/api/quick_capture_api.dart';
+import '../data/api/settings_api.dart';
 import '../data/api/tasks_api.dart';
 import '../data/repositories/auth_repository.dart';
 import '../data/repositories/chat_repository.dart';
@@ -85,3 +86,7 @@ final milestonesRepositoryProvider = Provider<MilestonesRepository>((ref) {
 final briefingApiProvider = Provider<BriefingApi>((ref) {
   return BriefingApi(ref.watch(dioProvider));
 });
+
+final settingsApiProvider = Provider<SettingsApi>((ref) {
+  return SettingsApi(ref.watch(dioProvider));
+});

pubspec.lock

@@ -169,6 +169,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.1.2"
+  equatable:
+    dependency: transitive
+    description:
+      name: equatable
+      sha256: "3e0141505477fd8ad55d6eb4e7776d3fe8430be8e497ccb1521370c3f21a3e2b"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.0.8"
   fake_async:
     dependency: transitive
     description:
@@ -299,6 +307,14 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_timezone:
+    dependency: "direct main"
+    description:
+      name: flutter_timezone
+      sha256: e8d63f50f2806a3a71a08697286a0369e1d8f0902961327810459871c0bb01c2
+      url: "https://pub.dev"
+    source: hosted
+    version: "5.0.2"
   flutter_web_plugins:
     dependency: transitive
     description: flutter
@@ -640,6 +656,54 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.3.0"
+  permission_handler:
+    dependency: "direct main"
+    description:
+      name: permission_handler
+      sha256: "59adad729136f01ea9e35a48f5d1395e25cba6cea552249ddbe9cf950f5d7849"
+      url: "https://pub.dev"
+    source: hosted
+    version: "11.4.0"
+  permission_handler_android:
+    dependency: transitive
+    description:
+      name: permission_handler_android
+      sha256: d3971dcdd76182a0c198c096b5db2f0884b0d4196723d21a866fc4cdea057ebc
+      url: "https://pub.dev"
+    source: hosted
+    version: "12.1.0"
+  permission_handler_apple:
+    dependency: transitive
+    description:
+      name: permission_handler_apple
+      sha256: f000131e755c54cf4d84a5d8bd6e4149e262cc31c5a8b1d698de1ac85fa41023
+      url: "https://pub.dev"
+    source: hosted
+    version: "9.4.7"
+  permission_handler_html:
+    dependency: transitive
+    description:
+      name: permission_handler_html
+      sha256: "38f000e83355abb3392140f6bc3030660cfaef189e1f87824facb76300b4ff24"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.1.3+5"
+  permission_handler_platform_interface:
+    dependency: transitive
+    description:
+      name: permission_handler_platform_interface
+      sha256: eb99b295153abce5d683cac8c02e22faab63e50679b937fa1bf67d58bb282878
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.3.0"
+  permission_handler_windows:
+    dependency: transitive
+    description:
+      name: permission_handler_windows
+      sha256: "1a790728016f79a41216d88672dbc5df30e686e811ad4e698bfc51f76ad91f1e"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.1"
   petitparser:
     dependency: transitive
     description:

pubspec.yaml

@@ -26,6 +26,7 @@ dependencies:
   flutter_inappwebview: ^6.1.5
   flutter_markdown_plus: ^1.0.7
   google_fonts: ^8.0.2
+  flutter_timezone: ^5.0.2
 
 dev_dependencies:
   flutter_test: