feat: Firebase Cloud Messaging push notifications

Backend:
- New user_fcm_tokens table (migration 010) for storing device tokens
- FCMService sends push via Firebase HTTP legacy API (server key from .env)
- POST /api/fcm/register endpoint for Android to register its FCM token
- AdminController::sendNotification() triggers FCM push after DB insert
- FCM config added to config.php

Android:
- Firebase Cloud Messaging service (ServerManagerFirebaseService)
  receives push notifications and shows them via NotificationHelper
- FCM token registered with backend on new token and on login
- google-services.json template (must be replaced with real Firebase config)
- firebase-setup.sh script with configuration instructions
- FCM dependency + google-services plugin added to Gradle
- Bump to v1.8.0 (versionCode 12)

install/firebase-setup.sh

@@ -0,0 +1,46 @@
+#!/bin/bash
+# Firebase Cloud Messaging setup script
+# =======================================
+#
+# This script creates placeholder files for FCM integration.
+# You must replace them with real values from your Firebase project.
+#
+# Steps to set up Firebase:
+#
+# 1. Go to https://console.firebase.google.com/ and create a project
+#    (or use an existing one)
+#
+# 2. Add an Android app to your Firebase project with package name:
+#    com.devlab.app
+#
+# 3. Download google-services.json and place it at:
+#    android/app/google-services.json
+#
+# 4. Go to Project Settings > Cloud Messaging and copy the
+#    Server key (legacy) or Cloud Messaging API key
+#
+# 5. Set the server key in .env:
+#    FCM_SERVER_KEY=your_server_key_here
+#
+# 6. OR place your Firebase Admin service account key at:
+#    config/firebase-service-account.json
+#    (for the OAuth-based API - more secure)
+#
+# The app will work without FCM configured; push notifications
+# simply won't be sent until Firebase is set up.
+#
+# ---
+
+echo "Firebase setup script"
+echo "====================="
+echo ""
+echo "To enable push notifications:"
+echo ""
+echo "1. Create a Firebase project: https://console.firebase.google.com"
+echo "2. Add Android app with package: com.devlab.app"
+echo "3. Download google-services.json → android/app/google-services.json"
+echo "4. Get Server Key from Cloud Messaging settings"
+echo "5. Add to .env: FCM_SERVER_KEY=your_key_here"
+echo ""
+echo "Without these steps, push notifications are disabled."
+echo "The app will continue to work using polling as fallback."