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/profile/presentation/profile_screen.dart

@@ -1,4 +1,4 @@
-// Version: 1.0.1 | Created: 2026-04-01
+// Version: 1.1.0 | Created: 2026-04-01 | Updated: 2026-04-02
 // Profile screen. Shows current user info and logout button.
 
 import 'package:flutter/material.dart';
@@ -6,7 +6,10 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../../../core/auth/auth_notifier.dart';
 import '../../../core/auth/auth_state.dart';
+import '../../../core/config/app_config.dart';
 import '../../../core/network/matrix_client.dart';
+import '../../../shared/utils/matrix_id.dart';
+import '../../../shared/widgets/matrix_avatar.dart';
 
 class ProfileScreen extends ConsumerWidget {
   const ProfileScreen({super.key, this.embedded = false});
@@ -24,14 +27,12 @@ class ProfileScreen extends ConsumerWidget {
       orElse: () => '',
     );
 
-    final displayName = client.userID != null
-        ? (client.userID!.split(':').first.replaceFirst('@', ''))
-        : 'Unknown';
+    final displayName = client.userID?.matrixLocalpart ?? 'Unknown';
 
     final body = ListView(
       padding: const EdgeInsets.all(24),
       children: [
-        _ProfileAvatar(displayName: displayName),
+        Center(child: MatrixAvatar(name: displayName, radius: 48)),
         const SizedBox(height: 16),
         Center(
           child: Text(
@@ -84,7 +85,7 @@ class ProfileScreen extends ConsumerWidget {
             ListTile(
               leading: const Icon(Icons.lock_outline),
               title: const Text('End-to-end encryption'),
-              subtitle: const Text('Active — messages are encrypted'),
+              subtitle: const Text('Setup coming in Phase 3'),
               enabled: false,
             ),
             ListTile(
@@ -112,7 +113,7 @@ class ProfileScreen extends ConsumerWidget {
         const SizedBox(height: 16),
         Center(
           child: Text(
-            'M8Chat 1.0.0 · matrix.m8chat.au',
+            '${AppConfig.appName} ${AppConfig.appVersion} · ${AppConfig.matrixServerName}',
             style: Theme.of(context).textTheme.bodySmall?.copyWith(
               color: Theme.of(context).colorScheme.onSurface.withAlpha(77),
             ),
@@ -130,34 +131,6 @@ class ProfileScreen extends ConsumerWidget {
   }
 }
 
-class _ProfileAvatar extends StatelessWidget {
-  const _ProfileAvatar({required this.displayName});
-
-  final String displayName;
-
-  @override
-  Widget build(BuildContext context) {
-    final initials = displayName.isNotEmpty
-        ? displayName[0].toUpperCase()
-        : '?';
-
-    return Center(
-      child: CircleAvatar(
-        radius: 48,
-        backgroundColor: Theme.of(context).colorScheme.primary.withAlpha(51),
-        child: Text(
-          initials,
-          style: TextStyle(
-            fontSize: 36,
-            fontWeight: FontWeight.bold,
-            color: Theme.of(context).colorScheme.primary,
-          ),
-        ),
-      ),
-    );
-  }
-}
-
 class _LogoutButton extends StatelessWidget {
   const _LogoutButton({required this.onLogout});
 
@@ -171,7 +144,9 @@ class _LogoutButton extends StatelessWidget {
           context: context,
           builder: (_) => AlertDialog(
             title: const Text('Sign out'),
-            content: const Text('Are you sure you want to sign out of M8Chat?'),
+            content: Text(
+              'Are you sure you want to sign out of ${AppConfig.appName}?',
+            ),
             actions: [
               TextButton(
                 onPressed: () => Navigator.of(context).pop(),