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/profile/presentation/profile_screen.dart

@@ -1,4 +1,4 @@
-// Version: 1.1.0 | Created: 2026-04-01 | Updated: 2026-04-02
+// Version: 1.4.0 | Created: 2026-04-01 | Updated: 2026-04-11
 // Profile screen. Shows current user info and logout button.
 
 import 'package:flutter/material.dart';
@@ -10,6 +10,8 @@ import '../../../core/config/app_config.dart';
 import '../../../core/network/matrix_client.dart';
 import '../../../shared/utils/matrix_id.dart';
 import '../../../shared/widgets/matrix_avatar.dart';
+import 'key_restore_dialog.dart';
+import 'security_setup_dialog.dart';
 
 class ProfileScreen extends ConsumerWidget {
   const ProfileScreen({super.key, this.embedded = false});
@@ -85,14 +87,57 @@ class ProfileScreen extends ConsumerWidget {
             ListTile(
               leading: const Icon(Icons.lock_outline),
               title: const Text('End-to-end encryption'),
-              subtitle: const Text('Setup coming in Phase 3'),
+              subtitle: Text(
+                client.encryptionEnabled
+                    ? 'Active — messages are encrypted'
+                    : 'Not available in this browser',
+              ),
               enabled: false,
             ),
             ListTile(
-              leading: const Icon(Icons.verified_user_outlined),
-              title: const Text('Verify devices'),
-              subtitle: const Text('Cross-signing setup — coming in Phase 2'),
-              enabled: false,
+              leading: const Icon(Icons.key_outlined),
+              title: const Text('Restore message keys'),
+              subtitle: const Text(
+                'Enter your recovery key to decrypt old messages',
+              ),
+              enabled: client.encryptionEnabled,
+              onTap: client.encryptionEnabled
+                  ? () async {
+                      final restored =
+                          await showKeyRestoreDialog(context, client);
+                      if (restored && context.mounted) {
+                        ScaffoldMessenger.of(context).showSnackBar(
+                          const SnackBar(
+                            content: Text('Keys restored — reopen rooms '
+                                'to see decrypted messages.'),
+                          ),
+                        );
+                      }
+                    }
+                  : null,
+            ),
+            ListTile(
+              leading: const Icon(Icons.shield_outlined),
+              title: const Text('Security setup'),
+              subtitle: Text(
+                client.encryption?.crossSigning.enabled == true
+                    ? 'Cross-signing active — device verified'
+                    : 'Set up cross-signing and key backup',
+              ),
+              enabled: client.encryptionEnabled,
+              onTap: client.encryptionEnabled
+                  ? () async {
+                      final completed =
+                          await showSecuritySetupDialog(context, client);
+                      if (completed && context.mounted) {
+                        ScaffoldMessenger.of(context).showSnackBar(
+                          const SnackBar(
+                            content: Text('Security setup complete.'),
+                          ),
+                        );
+                      }
+                    }
+                  : null,
             ),
             ListTile(
               leading: const Icon(Icons.password_outlined),