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/main.dart

@@ -1,15 +1,24 @@
-// Version: 1.0.1 | Created: 2026-04-01
+// Version: 1.1.0 | Created: 2026-04-01 | Updated: 2026-04-10
 // Application entry point.
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:olm/olm.dart' as olm;
 
 import 'app/app.dart';
 
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
 
+  // Check Olm availability — this prints to the browser console.
+  try {
+    await olm.init();
+    debugPrint('[M8Chat] Olm initialized successfully: ${olm.get_library_version()}');
+  } catch (e) {
+    debugPrint('[M8Chat] Olm NOT available: $e');
+  }
+
   // Catch Flutter framework errors (widget build, rendering) without crashing.
   FlutterError.onError = (details) {
     debugPrint('[M8Chat] Flutter error: ${details.exceptionAsString()}');