Add TWP Softphone Flutter app and complete mobile backend API

Backend: Add /voice/token endpoint with AccessToken + VoiceGrant for
mobile VoIP, implement unhold_call() with call leg detection, wire FCM
push notifications into call queue and webhook missed call handlers,
add data-only FCM message support for Android background wake, and add
Twilio API Key / Push Credential settings fields.

Flutter app: Full softphone with Twilio Voice SDK integration, JWT auth
with auto-refresh, SSE real-time queue updates, FCM push notifications,
Material 3 UI with dashboard, active call screen, dialpad, and call
controls (mute/speaker/hold/transfer).

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

mobile/android/app/build.gradle

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+plugins {
+    id "com.android.application"
+    id "kotlin-android"
+    id "dev.flutter.flutter-gradle-plugin"
+    id "com.google.gms.google-services"
+}
+
+android {
+    namespace = "io.cloudhosting.twp.twp_softphone"
+    compileSdk = flutter.compileSdkVersion
+    ndkVersion = flutter.ndkVersion
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_11
+        targetCompatibility = JavaVersion.VERSION_11
+    }
+
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_11
+    }
+
+    defaultConfig {
+        applicationId = "io.cloudhosting.twp.twp_softphone"
+        minSdkVersion 24
+        targetSdk = flutter.targetSdkVersion
+        versionCode = flutter.versionCode
+        versionName = flutter.versionName
+        multiDexEnabled true
+    }
+
+    buildTypes {
+        release {
+            signingConfig = signingConfigs.debug
+            minifyEnabled true
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+        }
+    }
+}
+
+flutter {
+    source = "../.."
+}
+
+dependencies {
+    implementation platform('com.google.firebase:firebase-bom:33.0.0')
+    implementation 'com.google.firebase:firebase-messaging'
+}

mobile/android/app/proguard-rules.pro

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+# Twilio Voice SDK
+-keep class com.twilio.** { *; }
+-keep class tvo.webrtc.** { *; }
+
+# Firebase
+-keep class com.google.firebase.** { *; }
+
+# Flutter
+-keep class io.flutter.** { *; }

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

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+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- The INTERNET permission is required for development. Specifically,
+         the Flutter tool needs it to communicate with the running application
+         to allow setting breakpoints, to provide hot reload, etc.
+    -->
+    <uses-permission android:name="android.permission.INTERNET"/>
+</manifest>

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

@@ -0,0 +1,65 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <!-- Audio/Phone permissions for VoIP -->
+    <uses-permission android:name="android.permission.RECORD_AUDIO"/>
+    <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS"/>
+    <uses-permission android:name="android.permission.BLUETOOTH"/>
+    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT"/>
+
+    <!-- Foreground service for active calls -->
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE"/>
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_PHONE_CALL"/>
+
+    <!-- Full screen intent for incoming calls on lock screen -->
+    <uses-permission android:name="android.permission.USE_FULL_SCREEN_INTENT"/>
+    <uses-permission android:name="android.permission.WAKE_LOCK"/>
+    <uses-permission android:name="android.permission.MANAGE_OWN_CALLS"/>
+
+    <!-- Push notifications -->
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS"/>
+
+    <!-- Internet -->
+    <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
+
+    <application
+        android:label="TWP Softphone"
+        android:name="${applicationName}"
+        android:icon="@mipmap/ic_launcher">
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:launchMode="singleTop"
+            android:taskAffinity=""
+            android:theme="@style/LaunchTheme"
+            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
+            android:hardwareAccelerated="true"
+            android:windowSoftInputMode="adjustResize"
+            android:showOnLockScreen="true"
+            android:turnScreenOn="true">
+            <meta-data
+              android:name="io.flutter.embedding.android.NormalTheme"
+              android:resource="@style/NormalTheme"
+              />
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN"/>
+                <category android:name="android.intent.category.LAUNCHER"/>
+            </intent-filter>
+            <!-- FCM click action -->
+            <intent-filter>
+                <action android:name="FLUTTER_NOTIFICATION_CLICK"/>
+                <category android:name="android.intent.category.DEFAULT"/>
+            </intent-filter>
+        </activity>
+        <meta-data
+            android:name="flutterEmbedding"
+            android:value="2" />
+    </application>
+
+    <queries>
+        <intent>
+            <action android:name="android.intent.action.PROCESS_TEXT"/>
+            <data android:mimeType="text/plain"/>
+        </intent>
+    </queries>
+</manifest>

mobile/android/app/src/main/java/io/cloudhosting/twp/twp_softphone/MainActivity.kt

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+package io.cloudhosting.twp.twp_softphone
+
+import io.flutter.embedding.android.FlutterActivity
+
+class MainActivity: FlutterActivity()

mobile/android/app/src/main/java/io/flutter/plugins/GeneratedPluginRegistrant.java

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+package io.flutter.plugins;
+
+import androidx.annotation.Keep;
+import androidx.annotation.NonNull;
+import io.flutter.Log;
+
+import io.flutter.embedding.engine.FlutterEngine;
+
+/**
+ * Generated file. Do not edit.
+ * This file is generated by the Flutter tool based on the
+ * plugins that support the Android platform.
+ */
+@Keep
+public final class GeneratedPluginRegistrant {
+  private static final String TAG = "GeneratedPluginRegistrant";
+  public static void registerWith(@NonNull FlutterEngine flutterEngine) {
+    try {
+      flutterEngine.getPlugins().add(new io.flutter.plugins.firebase.core.FlutterFirebaseCorePlugin());
+    } catch (Exception e) {
+      Log.e(TAG, "Error registering plugin firebase_core, io.flutter.plugins.firebase.core.FlutterFirebaseCorePlugin", e);
+    }
+    try {
+      flutterEngine.getPlugins().add(new io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingPlugin());
+    } catch (Exception e) {
+      Log.e(TAG, "Error registering plugin firebase_messaging, io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingPlugin", e);
+    }
+    try {
+      flutterEngine.getPlugins().add(new com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin());
+    } catch (Exception e) {
+      Log.e(TAG, "Error registering plugin flutter_local_notifications, com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin", e);
+    }
+    try {
+      flutterEngine.getPlugins().add(new com.it_nomads.fluttersecurestorage.FlutterSecureStoragePlugin());
+    } catch (Exception e) {
+      Log.e(TAG, "Error registering plugin flutter_secure_storage, com.it_nomads.fluttersecurestorage.FlutterSecureStoragePlugin", e);
+    }
+    try {
+      flutterEngine.getPlugins().add(new io.flutter.plugins.pathprovider.PathProviderPlugin());
+    } catch (Exception e) {
+      Log.e(TAG, "Error registering plugin path_provider_android, io.flutter.plugins.pathprovider.PathProviderPlugin", e);
+    }
+    try {
+      flutterEngine.getPlugins().add(new com.twilio.twilio_voice.TwilioVoicePlugin());
+    } catch (Exception e) {
+      Log.e(TAG, "Error registering plugin twilio_voice, com.twilio.twilio_voice.TwilioVoicePlugin", e);
+    }
+  }
+}

mobile/android/app/src/main/res/values/styles.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <style name="LaunchTheme" parent="@android:style/Theme.Light.NoTitleBar">
+        <item name="android:windowBackground">@android:color/white</item>
+    </style>
+    <style name="NormalTheme" parent="@android:style/Theme.Light.NoTitleBar">
+        <item name="android:windowBackground">@android:color/white</item>
+    </style>
+</resources>

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

@@ -0,0 +1,7 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- The INTERNET permission is required for development. Specifically,
+         the Flutter tool needs it to communicate with the running application
+         to allow setting breakpoints, to provide hot reload, etc.
+    -->
+    <uses-permission android:name="android.permission.INTERNET"/>
+</manifest>