Add FCM push notifications, queue alerts, caller ID fixes, and auto-revert agent status

Server-side:
- Add push credential auto-creation for FCM incoming call notifications
- Add queue alert FCM notifications (data-only for background delivery)
- Add queue alert cancellation on call accept/disconnect
- Fix caller ID to show caller's number instead of Twilio number
- Fix FCM token storage when refresh_token is null
- Add pre_call_status tracking to revert agent status 30s after call ends
- Add SSE fallback polling for mobile app connectivity

Mobile app:
- Add Android telecom permissions and phone account registration
- Add VoiceFirebaseMessagingService for incoming call push handling
- Add insistent queue alert notifications with custom sound
- Fix caller number display on active call screen
- Add caller ID selection dropdown on dashboard
- Add phone numbers endpoint and provider support
- Add unit tests for CallInfo, QueueState, and CallProvider
- Remove local.properties from tracking, add .gitignore

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

mobile/android/app/src/main/AndroidManifest.xml

@@ -51,6 +51,15 @@
                 <category android:name="android.intent.category.DEFAULT"/>
             </intent-filter>
         </activity>
+        <!-- Twilio Voice FCM handler — must have higher priority than Flutter's default -->
+        <service
+            android:name="com.twilio.twilio_voice.fcm.VoiceFirebaseMessagingService"
+            android:exported="false">
+            <intent-filter android:priority="10">
+                <action android:name="com.google.firebase.MESSAGING_EVENT" />
+            </intent-filter>
+        </service>
+
         <meta-data
             android:name="flutterEmbedding"
             android:value="2" />

mobile/android/local.properties

@@ -1,2 +0,0 @@
-flutter.sdk=/opt/flutter
-sdk.dir=/opt/android-sdk