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/calls/data/livekit_service.dart

@@ -1,10 +1,10 @@
-// Version: 1.3.0 | Created: 2026-04-01 | Updated: 2026-04-03
+// Version: 1.4.0 | Created: 2026-04-01 | Updated: 2026-04-10
 // LiveKitService — fetches a JWT from the Matrix server's /_matrix/livekit/jwt
 // endpoint, then connects a LiveKit Room using that token.
 //
-// The JWT endpoint is defined in AppConfig.livekitJwtUrl and uses the Matrix
-// access token as Bearer auth. The LiveKit server URL is the same host as the
-// Matrix server (as configured on chat.m8chat.au).
+// E2EE: Frame encryption is enabled via livekit_client's E2EEOptions.
+// Encryption keys are exchanged with Element X via m.rtc.encryption_keys
+// to-device events (see call_e2ee.dart).
 
 import 'dart:convert';
 import 'dart:math';
@@ -19,6 +19,7 @@ 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 'call_e2ee.dart';
 
 part 'livekit_service.g.dart';
 
@@ -67,6 +68,7 @@ class LiveKitService {
   Room? _activeRoom;
   String? _activeMatrixRoomId;
   String? _membershipId;
+  CallE2EEManager? _e2eeManager;
 
   Room? get activeRoom => _activeRoom;
 
@@ -111,14 +113,37 @@ class LiveKitService {
     _activeMatrixRoomId = matrixRoomId;
     debugPrint('[LiveKit] Call member state event sent');
 
-    // Step 3 — connect to LiveKit
-    final room = Room();
+    // Step 3 — initialise E2EE key exchange
+    _e2eeManager = CallE2EEManager(
+      client: client,
+      matrixRoomId: matrixRoomId,
+    );
+    final keyProvider = await _e2eeManager!.init();
+
+    // Step 4 — connect to LiveKit with frame encryption
+    // COOP/COEP headers on the server enable SharedArrayBuffer for the
+    // E2EE web worker. Without them the worker crashes.
+    final room = Room(
+      roomOptions: RoomOptions(
+        e2eeOptions: E2EEOptions(keyProvider: keyProvider),
+      ),
+    );
     try {
       await room.connect(livekitUrl, jwt);
       _activeRoom = room;
+
+      // Step 5 — set our local key and share with other participants
+      final localIdentity = room.localParticipant?.identity;
+      debugPrint('[LiveKit] Connected, local identity: $localIdentity');
+      if (localIdentity != null) {
+        await _e2eeManager!.setLocalKey(localIdentity);
+      }
+      await _e2eeManager!.sendKeyToParticipants();
+
       return LiveKitConnected(room: room);
     } on Exception catch (e) {
-      // Clean up the state event on failure
+      await _e2eeManager?.dispose();
+      _e2eeManager = null;
       await _clearCallMemberEvent(client, matrixRoomId, userId);
       await room.disconnect();
       await room.dispose();
@@ -136,6 +161,10 @@ class LiveKitService {
     _activeMatrixRoomId = null;
     _membershipId = null;
 
+    // Clean up E2EE key exchange
+    await _e2eeManager?.dispose();
+    _e2eeManager = null;
+
     // Step 1: Leave LiveKit — Element X will see us disappear from the SFU
     if (room != null) {
       await room.disconnect();
@@ -255,6 +284,7 @@ class LiveKitService {
   }
 
   /// Clear the call.member state event (remove our membership).
+  /// Element X expects empty content `{}` — not `{'memberships': []}`.
   Future<void> _clearCallMemberEvent(
     Client client,
     String matrixRoomId,
@@ -265,8 +295,9 @@ class LiveKitService {
         matrixRoomId,
         _kCallMemberEventType,
         userId,
-        {'memberships': []},
+        {},
       );
+      debugPrint('[LiveKit] Call member event cleared for $userId');
     } catch (e) {
       debugPrint('[LiveKit] Failed to clear call member event: $e');
     }