fix: export deduplication and PiP remote mute detection

Export: timeline.getEvents() returns the entire growing window on every
pagination step, causing the same events to be added multiple times.
Fixed by tracking seen eventIds in a Set and skipping duplicates.

PiP mute: replace silence-inference with real remote participant mute
state. EC renders a [data-muted] attribute per participant tile with
aria-label=userId. Watch attribute changes via MutationObserver,
filter out local user, show overlay when any remote is muted.

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

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

@@ -49,12 +49,18 @@ export function ExportRoomHistory({ requestClose }: ExportRoomHistoryProps) {
       };
 
       const collected: MsgRecord[] = [];
+      // timeline.getEvents() returns the entire growing window on every call,
+      // so we must deduplicate by eventId to avoid re-adding the same events
+      // on each pagination step.
+      const seen = new Set<string>();
       const timeline = room.getLiveTimeline();
       let canLoadMore = true;
 
-      // Collect events already in the live timeline
       const addEvents = (events: ReturnType<typeof timeline.getEvents>) => {
         for (const ev of events) {
+          const evId = ev.getId();
+          if (!evId || seen.has(evId)) continue;
+          seen.add(evId);
           if (ev.getType() !== EventType.RoomMessage) continue;
           if (ev.isDecryptionFailure()) continue;
           const ts = ev.getTs();
@@ -68,7 +74,7 @@ export function ExportRoomHistory({ requestClose }: ExportRoomHistoryProps) {
             ts,
             sender: ev.getSender() ?? '',
             body,
-            eventId: ev.getId() ?? '',
+            eventId: evId,
             msgtype,
           });
         }