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)

src/Services/FCMService.php

@@ -0,0 +1,131 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ServerManager\Services;
+
+use ServerManager\Core\App;
+use ServerManager\Core\Database;
+use ServerManager\Core\Logger;
+
+class FCMService
+{
+    private Database $db;
+    private Logger $logger;
+    private string $serverKey;
+
+    public function __construct()
+    {
+        $this->db = Database::getInstance();
+        $this->logger = Logger::getInstance();
+        $config = App::getConfig();
+
+        $this->serverKey = $config['fcm']['server_key'] ?? $_ENV['FCM_SERVER_KEY'] ?? '';
+    }
+
+    public function isConfigured(): bool
+    {
+        return !empty($this->serverKey);
+    }
+
+    public function sendToUser(int $userId, string $title, string $body, string $type = 'info', ?int $notificationId = null): bool
+    {
+        if (!$this->isConfigured()) {
+            return false;
+        }
+
+        $tokens = $this->db->fetchAll(
+            'SELECT token FROM user_fcm_tokens WHERE user_id = ?',
+            [$userId]
+        );
+
+        if (empty($tokens)) {
+            return false;
+        }
+
+        $success = true;
+        foreach ($tokens as $row) {
+            $result = $this->sendToDevice($row['token'], $title, $body, $type, $notificationId);
+            if (!$result) $success = false;
+        }
+
+        return $success;
+    }
+
+    public function sendToAll(string $title, string $body, string $type = 'info', ?int $notificationId = null): int
+    {
+        if (!$this->isConfigured()) {
+            return 0;
+        }
+
+        $tokens = $this->db->fetchAll('SELECT DISTINCT token FROM user_fcm_tokens');
+        if (empty($tokens)) return 0;
+
+        $sent = 0;
+        foreach ($tokens as $row) {
+            if ($this->sendToDevice($row['token'], $title, $body, $type, $notificationId)) {
+                $sent++;
+            }
+        }
+
+        return $sent;
+    }
+
+    private function sendToDevice(string $token, string $title, string $body, string $type, ?int $notificationId): bool
+    {
+        $payload = [
+            'to' => $token,
+            'priority' => 'high',
+            'notification' => [
+                'title' => $title,
+                'body' => $body,
+                'sound' => 'default',
+            ],
+            'data' => [
+                'type' => $type,
+                'notification_id' => (string) ($notificationId ?? 0),
+                'click_action' => 'OPEN_NOTIFICATIONS',
+            ],
+            'android' => [
+                'priority' => 'high',
+                'notification' => [
+                    'channel_id' => match ($type) {
+                        'error', 'warning' => 'notifications_alerts',
+                        default => 'notifications_general',
+                    },
+                    'priority' => match ($type) {
+                        'error' => 'high',
+                        default => 'default',
+                    },
+                    'sound' => 'default',
+                ],
+            ],
+        ];
+
+        $ch = curl_init('https://fcm.googleapis.com/fcm/send');
+        curl_setopt_array($ch, [
+            CURLOPT_POST => true,
+            CURLOPT_HTTPHEADER => [
+                'Content-Type: application/json',
+                'Authorization: key=' . $this->serverKey,
+            ],
+            CURLOPT_POSTFIELDS => json_encode($payload),
+            CURLOPT_RETURNTRANSFER => true,
+            CURLOPT_TIMEOUT => 15,
+        ]);
+
+        $response = curl_exec($ch);
+        $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
+        curl_close($ch);
+
+        if ($httpCode !== 200) {
+            $this->logger->error('FCM send failed', [
+                'http_code' => $httpCode,
+                'response' => substr($response, 0, 500),
+            ]);
+            return false;
+        }
+
+        return true;
+    }
+}