refactor(frontend): colocate admin components and split service layer

Move route-specific admin components from components/common/admin into
app/(main)/admin/<feature>/components/. Split AdminService god object into
domain services, fix UploadService to use BaseService, add AdminUploadService,
consolidate DB export into DbManageService, and migrate consumers to the
unified services entry.

frontend/lib/services/admin/auth-source.service.ts

@@ -0,0 +1,26 @@
+import {BaseService} from '@/lib/services/core';
+import type {AuthSource, AuthSourceRequest, ToggleAuthSourceRequest} from './types';
+
+export class AdminAuthSourceService extends BaseService {
+  protected static readonly basePath = '/api/v1/admin';
+
+  static async listAuthSources(): Promise<AuthSource[]> {
+    return this.get<AuthSource[]>('/auth-sources');
+  }
+
+  static async createAuthSource(request: AuthSourceRequest): Promise<AuthSource> {
+    return this.post<AuthSource>('/auth-sources', request);
+  }
+
+  static async updateAuthSource(id: string, request: AuthSourceRequest): Promise<AuthSource> {
+    return this.put<AuthSource>(`/auth-sources/${id}`, request);
+  }
+
+  static async toggleAuthSource(id: string, request: ToggleAuthSourceRequest): Promise<void> {
+    return this.put<void>(`/auth-sources/${id}/toggle`, request);
+  }
+
+  static async deleteAuthSource(id: string): Promise<void> {
+    return this.delete<void>(`/auth-sources/${id}`);
+  }
+}