feat: auto-refresh data on app resume and tab switch

- App resume: invalidates all main providers (conversations, calendar,
  news, knowledge, briefing) when the app returns to foreground.
  Throttled to once per 5 minutes to avoid hammering the server.
- Tab switch: refreshes the incoming tab's provider when navigating
  between Briefing / Knowledge / Conversations shell tabs.

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

lib/app.dart

@@ -11,6 +11,11 @@ import 'providers/api_client_provider.dart';
 import 'providers/auth_provider.dart';
 import 'providers/capture_queue_provider.dart';
 import 'providers/capture_work_queue_provider.dart';
+import 'providers/briefing_provider.dart';
+import 'providers/calendar_provider.dart';
+import 'providers/chat_provider.dart';
+import 'providers/knowledge_provider.dart';
+import 'providers/news_provider.dart';
 import 'providers/notes_provider.dart';
 import 'providers/settings_provider.dart';
 import 'providers/update_provider.dart';
@@ -182,16 +187,22 @@ class _Shell extends ConsumerStatefulWidget {
   ConsumerState<_Shell> createState() => _ShellState();
 }
 
-class _ShellState extends ConsumerState<_Shell> {
+class _ShellState extends ConsumerState<_Shell> with WidgetsBindingObserver {
   static const _tabs = [
     Routes.briefing,
     Routes.knowledge,
     Routes.conversations,
   ];
 
+  // Minimum gap between app-resume refreshes to avoid hammering the server.
+  static const _resumeCooldown = Duration(minutes: 5);
+  DateTime? _lastResumeRefresh;
+  int? _prevTabIndex;
+
   @override
   void initState() {
     super.initState();
+    WidgetsBinding.instance.addObserver(this);
     WidgetsBinding.instance.addPostFrameCallback((_) {
       // Silent update check — only if we haven't already checked this session.
       final repoUrl = ref.read(forgejoRepoUrlProvider);
@@ -206,6 +217,49 @@ class _ShellState extends ConsumerState<_Shell> {
     });
   }
 
+  @override
+  void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
+    super.dispose();
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (state != AppLifecycleState.resumed) return;
+    final now = DateTime.now();
+    if (_lastResumeRefresh != null &&
+        now.difference(_lastResumeRefresh!) < _resumeCooldown) {
+      return;
+    }
+    _lastResumeRefresh = now;
+    _refreshAll();
+  }
+
+  /// Refresh every major data provider. Safe to call speculatively —
+  /// providers that aren't currently watched are already disposed.
+  void _refreshAll() {
+    ref.invalidate(conversationsProvider);
+    ref.invalidate(calendarProvider);
+    ref.invalidate(newsProvider);
+    // Notifier (not AsyncNotifier) — needs explicit refresh call.
+    ref.read(knowledgeProvider.notifier).refresh();
+    // briefingProvider is an AsyncNotifier family; invalidating the family
+    // is safe even if no conversation is open.
+    ref.invalidate(briefingProvider);
+  }
+
+  /// Refresh only the provider backing the given shell tab index.
+  void _refreshTab(int index) {
+    switch (index) {
+      case 0:
+        ref.invalidate(briefingProvider);
+      case 1:
+        ref.read(knowledgeProvider.notifier).refresh();
+      case 2:
+        ref.invalidate(conversationsProvider);
+    }
+  }
+
   Future<void> _syncTimezone() async {
     try {
       final tzInfo = await FlutterTimezone.getLocalTimezone();
@@ -340,6 +394,13 @@ class _ShellState extends ConsumerState<_Shell> {
     });
     final location = GoRouterState.of(context).matchedLocation;
     final index = _tabIndex(location);
+
+    // Refresh the incoming tab's data when switching between shell tabs.
+    if (_prevTabIndex != null && _prevTabIndex != index && index < 3) {
+      WidgetsBinding.instance.addPostFrameCallback((_) => _refreshTab(index));
+    }
+    _prevTabIndex = index;
+
     final child = widget.child;
     final isWide = MediaQuery.of(context).size.width >= 600;