fix(api): correctly serialize roles list for admin user seeding

The admin user seeding was failing with a JSON syntax error because the `roles` list (`List<String>`) was being passed directly to the database driver for a `JSONB` column. The driver did not correctly serialize this into a valid JSON array string.

This change uses `jsonEncode` to explicitly convert the `roles` list into a correctly formatted JSON string before insertion, resolving the final startup error.

Author: fulleni

lib/src/services/database_seeding_service.dart

@@ -1,3 +1,4 @@
+import 'dart:convert';
 import 'package:ht_shared/ht_shared.dart';
 import 'package:logging/logging.dart';
 import 'package:postgres/postgres.dart';
@@ -353,7 +354,7 @@ class DatabaseSeedingService {
           parameters: {
             'id': adminUser.id,
             'email': adminUser.email,
-            'roles': adminUser.roles,
+            'roles': jsonEncode(adminUser.roles),
           },
         );