fix(call): ringtone loudness, caller decline notice, All-Muted badge

Three issues from live testing:
- A1: the 'classic' ringtone (call.ogg, mastered near full scale) was much
  louder than the synthesized styles. Attenuate it (CLASSIC_GAIN 0.45) so all
  ringtones sit at a comparable level.
- A3/A4: the caller had no indication when a DM/group callee declined — their
  UI kept "ringing" until the notification lifetime expired. IncomingCallListener
  now listens for RTCDecline events for a call we're hosting in the room and
  toasts the caller ("<name> declined your call").
- G1: the PiP "All muted" badge fired when any single remote participant muted.
  useRemoteAllMuted now returns true only when there is >=1 remote and every
  remote participant is muted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/hooks/useCallSpeakers.ts

@@ -145,13 +145,17 @@ export const useRemoteAllMuted = (callEmbed: CallEmbed | undefined): boolean =>
       // Each participant's mute icon has data-muted="true"|"false" and
       // aria-label set to their Matrix user ID.
       const muteIcons = doc.querySelectorAll<HTMLElement>('[data-muted]');
-      let anyRemoteMuted = false;
+      let remoteCount = 0;
+      let remoteMutedCount = 0;
       muteIcons.forEach((el) => {
         const userId = el.getAttribute('aria-label') ?? '';
         if (userId === localUserId) return;
-        if (el.getAttribute('data-muted') === 'true') anyRemoteMuted = true;
+        remoteCount += 1;
+        if (el.getAttribute('data-muted') === 'true') remoteMutedCount += 1;
       });
-      setMuted(anyRemoteMuted);
+      // "All muted" badge: true only when there is at least one remote
+      // participant and every one of them is muted (not merely any single one).
+      setMuted(remoteCount > 0 && remoteMutedCount === remoteCount);
     };
 
     let tileObserver: MutationObserver | undefined;