fix+feat: bug fixes, deleted message placeholder, poll display

Bug fixes:
- IncomingCallNotification: track ring setTimeout ID and clear it on
  cleanup/dismiss — prevents orphaned callbacks after unmount
- RoomTimeline: allow redacted m.room.message, m.room.encrypted and
  m.sticker events past the early-return filter so they hit the
  existing RedactedContent renderer showing the trash-icon placeholder

New features:
- PollContent component: read-only display of m.poll.start and
  org.matrix.msc3381.poll.start events (both stable Matrix 1.7 and
  MSC3381 unstable content keys); renders poll question + answer
  options inside the standard Message bubble; registered both as
  top-level event renderers and inside EncryptedContent callback
  so encrypted polls also render after decryption
- Deleted message placeholder: m.room.message and m.room.encrypted
  redacted events now show the existing MessageDeletedContent
  component (trash icon + italic notice) instead of disappearing
  entirely — matches Element, FluffyChat, Commet, Nheko behaviour

src/app/components/IncomingCallNotification.tsx

@@ -42,24 +42,27 @@ function useRingTone(active: boolean) {
       osc.stop(t + dur);
     };
 
+    let ringTimer: ReturnType<typeof setTimeout> | null = null;
     const ring = () => {
       if (cancelled) return;
       const now = ctx.currentTime;
       pulse(now, 880, 0.18);
       pulse(now + 0.28, 880, 0.18);
-      setTimeout(ring, 2200);
+      ringTimer = setTimeout(ring, 2200);
     };
 
     ring();
 
-    stopRef.current = () => {
+    const stop = () => {
       cancelled = true;
+      if (ringTimer !== null) clearTimeout(ringTimer);
       ctx.close();
     };
 
+    stopRef.current = stop;
+
     return () => {
-      cancelled = true;
-      ctx.close();
+      stop();
       stopRef.current = null;
     };
   }, [active]);