Phase 3.2 docs + Phase 3.1 testing fixes

- Add phase3.2.md requirement: overlay UX, mitra activity log
- Add phase3.2-plan.md implementation plan
- Fix stale request validation: add GET /:sessionId/status endpoint
- Fix notification tap flow: setIncomingFromNotification + onChatRequestTapped
- IncomingRequestSheet shows stale message instead of auto-dismiss
- Home screen validates on resume, shows immediately on fresh WS

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

mitra_app/lib/core/notifications/notification_service.dart

@@ -8,6 +8,10 @@ class NotificationService {
   static final _localNotifications = FlutterLocalNotificationsPlugin();
   static GoRouter? _router;
 
+  /// Callback for when a chat request notification is tapped.
+  /// Set this from the app to bridge notifications → Riverpod state.
+  static void Function(String sessionId)? onChatRequestTapped;
+
   static const _channel = AndroidNotificationChannel(
     'chat_messages',
     'Chat Messages',
@@ -119,8 +123,9 @@ class NotificationService {
     final type = data['type'] as String?;
     final action = data['action'] as String?;
 
-    if (type == 'chat_request' && action == 'open_accept') {
-      // Navigate to home where incoming request sheet will show
+    if (type == 'chat_request' && action == 'open_accept' && sessionId != null) {
+      // Update the notifier state with this session, then navigate
+      onChatRequestTapped?.call(sessionId);
       _router!.go('/home');
     } else if (type == 'session_closing' || type == 'session_expired') {
       // Navigate to the chat session closure screen