feat: Phase 3 — E2EE calls, Jitsi conferencing, help tab, web security model

- LiveKit call E2EE: CallE2EEManager exchanges encryption keys via Matrix
  to-device events (m.rtc.encryption_keys) for interop with Element X
- Olm bootstrapped in index.html before Flutter init; main.dart logs result
- Encrypted messages shown with lock icon and informative fallback text
- Profile screen: key restore dialog + security setup (cross-signing/backup)
- Jitsi feature: welcome screen (public, no login), conference tab, full-screen
  embed via JitsiMeetExternalAPI, JitsiLink parser for all common link formats
- Help tab: expandable cards for encryption, video calls, account management
- Web security model: no session persistence — device ID only across visits
- Media auth: MSC3916 authenticated endpoint for avatars (Synapse 1.120+)
- Router: welcome route as public landing page; jitsi route as public
- Manifest/index.html: M8Chat branding, dark theme colours

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

lib/features/rooms/data/rooms_repository.dart

@@ -2,6 +2,7 @@
 // Rooms repository. Reads room list from the Matrix SDK client.
 
 import 'package:matrix/matrix.dart';
+import 'package:flutter/foundation.dart';
 import 'package:riverpod_annotation/riverpod_annotation.dart';
 
 import '../../../core/network/matrix_client.dart';
@@ -24,6 +25,10 @@ class RoomsRepository {
   /// Returns the current room list, sorted unread-first then by last activity.
   List<RoomModel> getRooms() {
     final rooms = _client.rooms;
+    debugPrint('[Rooms] client.rooms count: ${rooms.length}');
+    for (final r in rooms) {
+      debugPrint('[Rooms]   ${r.id} "${r.getLocalizedDisplayname()}" isSpace=${r.isSpace}');
+    }
     final models = rooms.map(_toModel).toList();
 
     models.sort((a, b) {