Remove Twilio Push Credential references and add real Firebase config

All FCM push notifications are handled by WordPress backend (TWP_FCM),
so Twilio Push Credentials are unnecessary. Also replaces placeholder
google-services.json with real Firebase project config (twp-softphone).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

mobile/android/app/google-services.json

@@ -1,13 +1,13 @@
 {
   "project_info": {
-    "project_number": "000000000000",
-    "project_id": "twp-softphone-placeholder",
-    "storage_bucket": "twp-softphone-placeholder.appspot.com"
+    "project_number": "187457540438",
+    "project_id": "twp-softphone",
+    "storage_bucket": "twp-softphone.firebasestorage.app"
   },
   "client": [
     {
       "client_info": {
-        "mobilesdk_app_id": "1:000000000000:android:0000000000000000",
+        "mobilesdk_app_id": "1:187457540438:android:d6d777270c23f6660946f7",
         "android_client_info": {
           "package_name": "io.cloudhosting.twp.twp_softphone"
         }
@@ -15,7 +15,7 @@
       "oauth_client": [],
       "api_key": [
         {
-          "current_key": "PLACEHOLDER_API_KEY"
+          "current_key": "AIzaSyAdGJrWPy9b9arqHnlY5G_hsGiDcm6cchA"
         }
       ],
       "services": {