feat: PiP mute indicator, export history, activity log, unverified device warning

- PiP call window: mute overlay using MutationObserver on EC iframe's
  [data-testid="incall_mute"] button (data-kind="primary" = muted),
  same pattern as screenshare detection in CallControl.ts

- P2-4 Export Room History: new tab in room settings — Plain Text / JSON /
  HTML formats, optional date range, progress counter, paginated via
  paginateEventTimeline, blob download; E2EE-aware (skips failed decryptions)

- P2-6 Room Activity Log: new tab in room settings — filterable log of
  m.room.member, m.room.power_levels, m.room.name/topic/avatar/server_acl
  events with human-readable descriptions, relative timestamps, Load More
  pagination

- P2-10 Unverified Device Warning: warnOnUnverifiedDevices setting (default
  off); Warning.Container banner above composer in encrypted rooms with
  unverified devices; toggle in Settings → General → Privacy

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/room-settings/RoomSettings.tsx

@@ -17,6 +17,8 @@ import { Permissions } from './permissions';
 import { RoomSettingsPage } from '../../state/roomSettings';
 import { useRoom } from '../../hooks/useRoom';
 import { DeveloperTools } from '../common-settings/developer-tools';
+import { ExportRoomHistory } from './ExportRoomHistory';
+import { RoomActivityLog } from './RoomActivityLog';
 
 type RoomSettingsMenuItem = {
   page: RoomSettingsPage;
@@ -52,6 +54,16 @@ const useRoomSettingsMenuItems = (): RoomSettingsMenuItem[] =>
         name: 'Developer Tools',
         icon: Icons.Terminal,
       },
+      {
+        page: RoomSettingsPage.ExportPage,
+        name: 'Export',
+        icon: Icons.Download,
+      },
+      {
+        page: RoomSettingsPage.ActivityLogPage,
+        name: 'Activity',
+        icon: Icons.RecentClock,
+      },
     ],
     [],
   );
@@ -172,6 +184,12 @@ export function RoomSettings({ initialPage, requestClose }: RoomSettingsProps) {
       {activePage === RoomSettingsPage.DeveloperToolsPage && (
         <DeveloperTools requestClose={handlePageRequestClose} />
       )}
+      {activePage === RoomSettingsPage.ExportPage && (
+        <ExportRoomHistory requestClose={handlePageRequestClose} />
+      )}
+      {activePage === RoomSettingsPage.ActivityLogPage && (
+        <RoomActivityLog requestClose={handlePageRequestClose} />
+      )}
     </PageRoot>
   );
 }