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/utils/ringtones.ts

@@ -102,12 +102,17 @@ const playPhrase = (style: SynthStyle, volume: number, destination: AudioNode):
   });
 };
 
+// The bundled call.ogg is mastered near full scale, so at equal `volume` it is
+// perceptibly much louder than the synthesized styles (which peak at ~0.12–0.3).
+// Attenuate it so all ringtones sit at a comparable loudness.
+const CLASSIC_GAIN = 0.45;
+
 const startClassic = (volume: number, loop: boolean): (() => void) => {
   let audio: HTMLAudioElement | undefined;
   try {
     audio = new Audio(CallSound);
     audio.loop = loop;
-    audio.volume = clamp01(volume);
+    audio.volume = clamp01(volume) * CLASSIC_GAIN;
     audio.play().catch(() => undefined);
   } catch {
     audio = undefined;