fix(calls): only cancel-push unanswered calls; add native-call telemetry

- Re-ring on disconnect: sendCallCancel now only fires for UNANSWERED calls. An answered
  call ends via the WS event on both (awake) sides; a cancel push was re-ringing the
  device that just hung up.
- Native-call telemetry (temporary): the plugin fires callConnected/callError on its
  LiveKit connection; the WebView reports nc-answer/nc-connected/nc-error/nc-end/
  nc-outgoing to /api/push-debug so we can see from server logs whether the native room
  actually connects (no device console available). Served — no rebuild needed.

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

server/calls.js

@@ -145,8 +145,10 @@ async function endDmCallByRoom(room, silent) {
     call.users.forEach((uid) => { try { CHAT.pushToUser(uid, { type: 'chat-message', message: dto }); } catch (_) {} });
   } catch (_) {}
   call.users.forEach((uid, i) => { try { CHAT.pushToUser(uid, { type: 'dm-call', active: false, uuid: call.uuid, with: call.users[1 - i], room }); } catch (_) {} });
-  // Stop any CallKit ring on a killed/backgrounded device (no WS to receive the dm-call above).
-  try { for (const uid of call.users) PUSH.sendCallCancel(uid, call.uuid); } catch (_) {}
+  // Stop the CallKit ring on a device that's still RINGING (unanswered) — a killed/asleep callee has no WS
+  // to receive the dm-call above. For an ANSWERED call both sides are awake (the WS event ends it), and a
+  // cancel push would re-ring the device that just hung up — so only cancel when it was NOT answered.
+  if (!call.answered) { try { for (const uid of call.users) PUSH.sendCallCancel(uid, call.uuid); } catch (_) {} }
   // Missed-call banner to the callee (a plain notification, like a phone's missed call) when the call ended
   // UNANSWERED — timeout or the caller hung up before pickup. Skipped on decline (silent): they chose to.
   if (!silent && !call.answered) {