feat(call): Discord-style polish pass (groups A-C)

A — Call core:
- Deafen now implies mute + remembers pre-deafen mic state so un-deafen
  restores it (Discord-parity). Peers still see the headphones-off +
  mic-off badges in sync via the existing data-channel broadcast.
- Self-join sound fires on the local peer's r.connect() too, not just
  on remote ParticipantConnected, so the user gets the "I'm in" cue.
- New CallState.reconnecting holds the UI steady when LiveKit drops the
  signaling socket and retries; duration keeps ticking, status label
  switches to "Verbinde neu…". Full teardown only on terminal
  Disconnected (after LK gives up).
- joinActiveCall falls back to connected after 5s if no peer arrived —
  avoids hanging in "Verbinde…" when peers left the room mid-rejoin.

B — Ringtone:
- Oscillator base gain up (incoming 0.22 -> 0.4, outgoing 0.14 -> 0.22)
  so the default pattern survives laptop speakers + background music.
- New ringtoneVolume slider in Settings, default 0.9, live-applies to
  both the oscillator fallback and the custom-file <audio> element.

C — Participant tile:
- Split the speaking indicator: video tiles get the emerald border +
  inset glow; audio tiles rely on the existing avatar pulse. No more
  double-chrome when someone talks in grid/focus view.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop/src/components/CallUI.tsx

@@ -158,6 +158,7 @@ function PipCall() {
   const active =
     state.kind === 'connected' ||
     state.kind === 'connecting' ||
+    state.kind === 'reconnecting' ||
     state.kind === 'outgoing';
   if (!active) return null;