refactor: /simplify — 22 fixes from 3-agent code review

Critical:
- Fix MXC URI resolution: all avatars/images now resolve mxc:// to HTTP
- Sync persistence: only write changed rooms, batch message upserts
- lastActivityAt uses room.lastEvent.originServerTs, not creation time

High:
- Shared MatrixAvatar widget replaces 6 duplicate implementations
- CallScreen decodes roomId before LiveKit JWT fetch
- Decline button actually dismisses incoming call overlay
- EventTypes constants replace raw string literals
- LiveKitService uses lazy auth reads, onDispose disconnects

Medium:
- CallController is keepAlive with timer/room cleanup
- authRepository is keepAlive (used from keepAlive notifier)
- StreamController not closed in stopListening (crash fix)
- Index on messages.roomId for query performance
- 400ms debounce on user search
- Static DateFormat in MessageBubble
- Hardcoded strings replaced with AppConfig refs
- Duplicate isDirectMessage field removed from RoomModel
- E2EE profile claim corrected to Phase 3

Shared utilities:
- lib/shared/widgets/matrix_avatar.dart
- lib/shared/utils/mxc_url.dart
- lib/shared/utils/room_preview.dart
- lib/shared/utils/matrix_id.dart

rawJson column removed (unused, caused main-thread jsonEncode)
Schema migrated to v2 with roomId index.

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

lib/features/calls/data/livekit_service.dart

@@ -1,4 +1,4 @@
-// Version: 1.1.0 | Created: 2026-04-01
+// Version: 1.2.0 | Created: 2026-04-01 | Updated: 2026-04-02
 // LiveKitService — fetches a JWT from the Matrix server's /_matrix/livekit/jwt
 // endpoint, then connects a LiveKit Room using that token.
 //
@@ -54,9 +54,9 @@ final class LiveKitFailed extends LiveKitResult {
 
 /// Manages LiveKit room connections for MatrixRTC.
 class LiveKitService {
-  LiveKitService({required AuthState authState}) : _authState = authState;
+  LiveKitService({required Ref ref}) : _ref = ref;
 
-  final AuthState _authState;
+  final Ref _ref;
   Room? _activeRoom;
 
   Room? get activeRoom => _activeRoom;
@@ -67,7 +67,7 @@ class LiveKitService {
   /// 1. GET `/_matrix/livekit/jwt?roomId={id}&userId={id}`
   /// 2. Use returned token + LiveKit WS URL to connect a [Room]
   Future<LiveKitResult> connect(String matrixRoomId) async {
-    final auth = _authState;
+    final auth = _ref.read(authProvider);
     if (auth is! AuthAuthenticated) {
       return const LiveKitFailed(LiveKitNotAuthenticated());
     }
@@ -94,6 +94,7 @@ class LiveKitService {
       _activeRoom = room;
       return LiveKitConnected(room: room);
     } on Exception catch (e) {
+      await room.disconnect();
       await room.dispose();
       return LiveKitFailed(LiveKitConnectFailed(e.toString()));
     }
@@ -101,9 +102,12 @@ class LiveKitService {
 
   /// Disconnect and dispose the active room.
   Future<void> disconnect() async {
-    await _activeRoom?.disconnect();
-    await _activeRoom?.dispose();
+    final room = _activeRoom;
     _activeRoom = null;
+    if (room != null) {
+      await room.disconnect();
+      await room.dispose();
+    }
   }
 
   Future<_JwtFetchResult> _fetchJwt({
@@ -159,6 +163,7 @@ final class _JwtError extends _JwtFetchResult {
 
 @Riverpod(keepAlive: true)
 LiveKitService liveKitService(Ref ref) {
-  final authState = ref.watch(authProvider);
-  return LiveKitService(authState: authState);
+  final service = LiveKitService(ref: ref);
+  ref.onDispose(() async => service.disconnect());
+  return service;
 }