feat(ios): native CallKit + PushKit VoIP calling plugin + web bridge

The native call feature (iOS). Backward-compatible: without the plugin (current
builds) nativeCallOn() is false and every CallKit branch is skipped, so web/older
builds behave exactly as before.

Native (mobile/plugins/native-call, a local Capacitor plugin like audio-route):
- PushKit: registers for VoIP pushes, reports the VoIP token to JS (-> /api/v1/devices
  'ios-voip'). On an incoming VoIP push, reports a CallKit incoming call (full-screen
  ring, works when the app is force-killed).
- CallKit: answer/decline/end -> events to JS; configures the call AVAudioSession on
  didActivate so the WebView's WebRTC audio rides a call-priority session (background).
- Outgoing calls register with CallKit too (reportOutgoingCall) so they get the same
  active-call background-audio context.
- NativeCall.podspec (frameworks CallKit/PushKit/AVFoundation); added to mobile deps;
  ios-patch.sh now sets UIBackgroundModes = [audio, voip] (voip required for PushKit).

Web bridge (home.html): setupNativeCall() registers the VoIP token, joins on CallKit
answer, leaves/declines on CallKit end; on CallKit devices the in-app call-invite popup
+ WebAudio ring are suppressed (the system rings instead); outgoing calls are reported
to CallKit; call-end events dismiss the CallKit call. calls.js threads a stable call
uuid through the dm-call/group-call WS events + start responses so both sides can match
the CallKit call.

Needs a Codemagic build to compile the plugin; first on-device iteration expected.

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

mobile/plugins/native-call/package.json

@@ -0,0 +1,26 @@
+{
+  "name": "native-call",
+  "version": "1.0.0",
+  "description": "Native CallKit + PushKit VoIP calling for Biz Connect (iOS)",
+  "main": "dist/plugin.cjs.js",
+  "module": "dist/esm/index.js",
+  "types": "dist/esm/index.d.ts",
+  "author": "BizGaze",
+  "license": "MIT",
+  "files": [
+    "dist/",
+    "ios/",
+    "NativeCall.podspec"
+  ],
+  "capacitor": {
+    "ios": {
+      "src": "ios"
+    }
+  },
+  "devDependencies": {
+    "@capacitor/core": "^7.0.0"
+  },
+  "peerDependencies": {
+    "@capacitor/core": "^7.0.0"
+  }
+}