feat: implement testing notification on invitation acceptance

lib/services/notification_service.dart

@@ -275,6 +275,66 @@ class NotificationService {
     }
   }
 
+  Future<bool> sendNotificationToToken(
+    String token,
+    String title,
+    String body, {
+    Map<String, String>? data,
+  }) async {
+    try {
+      final accessToken = await _getAccessToken();
+      if (accessToken == null) {
+        print('Failed to get access token. Cannot send notifications.');
+        return false;
+      }
+
+      final url = Uri.parse('https://fcm.googleapis.com/v1/projects/$_projectId/messages:send');
+      final headers = {
+        'Content-Type': 'application/json',
+        'Authorization': 'Bearer $accessToken',
+      };
+
+      final payload = {
+        'message': {
+          'token': token,
+          'notification': {
+            'title': title,
+            'body': body,
+          },
+          'data': data ?? {},
+          'webpush': {
+            'notification': {
+              'icon': 'icons/ios/192.png',
+              'badge': 'icons/ios/192.png',
+            },
+          },
+        },
+      };
+
+      print('Sending notification to token: ${token.substring(0, 20)}...');
+      print('Payload: ${json.encode(payload)}');
+
+      final response = await http.post(
+        url,
+        headers: headers,
+        body: json.encode(payload),
+      );
+
+      if (response.statusCode == 200) {
+        print('Notification sent successfully to token!');
+        print('Response: ${response.body}');
+        return true;
+      } else {
+        print('Failed to send notification. Status: ${response.statusCode}');
+        print('Response: ${response.body}');
+        return false;
+      }
+    } catch (e) {
+      print('Error sending notification: $e');
+      return false;
+    }
+  }
+
   Future<bool> sendNotificationToTopic(
     String topic,
     String title,
@@ -333,8 +393,11 @@ class NotificationService {
   }
 
   Future<bool> sendCoffeeInviteAcceptedNotification() async {
-    return await sendNotificationToTopic(
-      'all',
+    // Send to specific token for testing
+    const testToken = 'cetNA4PmdzwBS075-zdvbP:APA91bEDAqLC0D4txAaiYAdzzfk43yk99tKlC_x3Tii24qHdyhIzuQifsJG4Rm_oijvdVkbsoQUm3tQso34_71OvU-kQsqZTrMOQVIvHkIul7PYqOODFJUA';
+    
+    return await sendNotificationToToken(
+      testToken,
       'Coffee Time! ☕',
       'You\'re set for coffee! Your invitation has been accepted.',
       data: {