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/RingtoneSettings.tsx

@@ -1,6 +1,11 @@
 import { useCallback, useEffect, useRef, useState } from 'react';
 import { useTranslation } from 'react-i18next';
 
+import {
+  getAudioSettings,
+  subscribeAudioSettings,
+  updateAudioSettings,
+} from '../lib/audioSettings';
 import {
   clearIncomingRingtone,
   getIncomingRingtone,
@@ -30,6 +35,10 @@ export function RingtoneSettings({ disabled = false }: Props) {
   const [busy, setBusy] = useState(false);
   const [playing, setPlaying] = useState(false);
   const [error, setError] = useState<string | null>(null);
+  const [volume, setVolume] = useState<number>(() => getAudioSettings().ringtoneVolume);
+
+  // Subscribe so cross-tab / in-call slider moves stay in sync here too.
+  useEffect(() => subscribeAudioSettings((s) => setVolume(s.ringtoneVolume)), []);
 
   const refresh = useCallback(async () => {
     try {
@@ -128,7 +137,7 @@ export function RingtoneSettings({ disabled = false }: Props) {
     const url = URL.createObjectURL(current.blob);
     const el = new Audio(url);
     el.loop = false;
-    el.volume = 0.85;
+    el.volume = volume;
     el.onended = () => stopPreview();
     el.onerror = () => {
       setError(
@@ -233,6 +242,36 @@ export function RingtoneSettings({ disabled = false }: Props) {
         </p>
       )}
 
+      <div className="flex items-center gap-3">
+        <label
+          htmlFor="ringtone-volume"
+          className="shrink-0 text-xs font-medium text-fg-muted"
+        >
+          {t('app:settings.ringtone_volume', { defaultValue: 'Lautstärke' })}
+        </label>
+        <input
+          id="ringtone-volume"
+          type="range"
+          min={0}
+          max={1}
+          step={0.01}
+          value={volume}
+          onChange={(e) => {
+            const v = Number(e.target.value);
+            setVolume(v);
+            updateAudioSettings({ ringtoneVolume: v });
+            // Apply to the currently-playing preview so the user hears the
+            // slider effect immediately while dragging.
+            if (previewRef.current) previewRef.current.volume = v;
+          }}
+          aria-label={t('app:settings.ringtone_volume', { defaultValue: 'Lautstärke' })}
+          className="flex-1 accent-accent"
+        />
+        <span className="w-10 shrink-0 text-right text-xs tabular-nums text-fg-muted">
+          {Math.round(volume * 100)}%
+        </span>
+      </div>
+
       <p className="text-[11px] text-fg-muted">
         {t('app:settings.ringtone_hint', {
           defaultValue: