feat: align with Gelbooru DAPI spec, optimize tag queries & batch categorization (v2.3.2)

test/backend/gelbooru_dapi_test.dart

@@ -0,0 +1,45 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:gel_rule_app/backend/models/content_provider_config.dart';
+import 'package:gel_rule_app/backend/providers/gelbooru_provider.dart';
+import 'package:gel_rule_app/backend/providers/provider_factory.dart';
+import 'package:gel_rule_app/core/http/dio_client.dart';
+
+void main() {
+  test('ProviderFactory creates GelbooruProvider with query credentials', () {
+    final factory = ProviderFactory();
+    final config = ContentProviderConfig(
+      id: 'gelbooru',
+      name: 'Gelbooru',
+      baseUrl: 'https://gelbooru.com',
+      apiType: 'gelbooru',
+      enabled: true,
+      priority: 10,
+      timeoutSeconds: 20,
+      customHeaders: const {
+        'query.api_key': 'test_api_key',
+        'query.user_id': '123456',
+      },
+      createdAt: DateTime(2026),
+      updatedAt: DateTime(2026),
+    );
+
+    final provider = factory.create(config);
+    expect(provider, isA<GelbooruProvider>());
+    final gelbooru = provider as GelbooruProvider;
+    expect(gelbooru.id, 'gelbooru');
+    expect(gelbooru.queryParameters['api_key'], 'test_api_key');
+    expect(gelbooru.queryParameters['user_id'], '123456');
+  });
+
+  test('GelbooruProvider mediaHeaders contains Referer and User-Agent', () {
+    final client = DioClient(baseUrl: 'https://gelbooru.com');
+    final provider = GelbooruProvider(
+      id: 'gelbooru',
+      name: 'Gelbooru',
+      baseUrl: 'https://gelbooru.com',
+      dioClient: client,
+    );
+
+    expect(provider.baseUrl, 'https://gelbooru.com');
+  });
+}