Android calls: professional incoming UI + killed-state ring reliability

Addresses on-device feedback from Increment 1:
- #2 Professional incoming screen: IncomingCallActivity redesigned — brand-
  blue backdrop, circular avatar with the caller's initial, name + call
  type, and two round icon buttons (red hang-up = Decline, green phone =
  Accept) instead of the full-screen colored buttons. New vector drawables
  ic_call_answer / ic_call_decline (also used on the notification actions).
- #1 Killed-state ring: the missed-call notification arriving while killed
  proves FCM reaches the app, so the ring (high-priority DATA) is being
  held by OEM battery management (OnePlus/Oppo Doze) until the call is over.
  Added REQUEST_IGNORE_BATTERY_OPTIMIZATIONS + a requestCallReliability()
  plugin method that prompts the "allow background activity" dialog once;
  the web calls it on Android call setup. (OEM auto-launch is a manual
  toggle with no API — guide the user.)

#3 (speaker/Bluetooth) and #4 (background audio) ride Increment 2 (native
LiveKit Android media + foreground service) — kept separate so the LiveKit
dependency can't block these UI/reliability fixes (the iOS coupling lesson).

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

mobile/plugins/native-call/android/src/main/AndroidManifest.xml

@@ -6,6 +6,9 @@
     <uses-permission android:name="android.permission.USE_FULL_SCREEN_INTENT" />
     <uses-permission android:name="android.permission.VIBRATE" />
     <uses-permission android:name="android.permission.WAKE_LOCK" />
+    <!-- Ask to be exempt from battery optimization so high-priority FCM call-wakes reach the app when it's
+         been swiped away / Dozing (OnePlus/Oppo hold data messages otherwise → the ring arrives too late). -->
+    <uses-permission android:name="android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS" />
 
     <application>
         <!-- Our FirebaseMessagingService REPLACES the @capacitor/push-notifications one: it handles call-wake