feat(calls): CallKit kill-switch + fix ~1s re-ring on cancel

MIC BROKEN with CallKit: a CallKit call reserves the microphone, so the WebView's
WebRTC can't capture it — calls are unusable until native LiveKit media lands. Add a
server kill-switch (CALLKIT_ENABLED, default OFF) so CallKit can be flipped without an
app rebuild: /api/meetings/config now returns callkit; setupNativeCall bails when off
(-> WebView calls, mic works); push.js only sends VoIP/CallKit pushes when enabled.
Deploying with the flag unset immediately restores working WebView calls.

RE-RING: a late cancel push for an already-declined call hit the plugin's 'unknown
uuid' path and re-reported a fresh incoming call (~1s re-ring). Track endedCalls and
make a late cancel for an already-ended call a no-op.

Server part deploys now (no rebuild); plugin re-ring fix ships with the native build.

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

server/public/home.html

@@ -3785,6 +3785,10 @@ function nativeCallPlugin(){ const P=window.Capacitor&&window.Capacitor.Plugins;
 function nativeCallOn(){ return _callkitReady; }
 async function setupNativeCall(){
   const NC=nativeCallPlugin(); if(!NC) return;
+  // Server kill-switch: only take over calls with CallKit when the server enables it (callkit:true). When
+  // off, calls use the WebView flow (mic works). Flipped on only once native media carries the audio.
+  let cfg={}; try{ cfg=await fetch('/api/meetings/config').then(r=>r.json()); }catch(_){}
+  if(!cfg || !cfg.callkit){ console.log('[callkit] disabled by server — using WebView calls'); return; }
   _callkitReady=true;
   // VoIP (PushKit) token → register as an 'ios-voip' device so the server sends CallKit wake pushes.
   NC.addListener('voipToken', (e)=>{ const token=e&&e.token; if(!token) return; postJSON('/api/v1/devices',{ platform:'ios-voip', token }).then(()=>console.log('[callkit] voip token registered')).catch((err)=>console.warn('[callkit] voip register failed', err)); });