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/user.service.ts

@@ -0,0 +1,32 @@
+import {BaseService} from '@/lib/services/core';
+import type {
+  AdminUser,
+  CreateUserRequest,
+  ListUsersRequest,
+  ListUsersResponse,
+  UpdateUserStatusRequest,
+} from './types';
+
+export class AdminUserService extends BaseService {
+  protected static readonly basePath = '/api/v1/admin';
+
+  static async listUsers(request: ListUsersRequest): Promise<ListUsersResponse> {
+    return this.get<ListUsersResponse>('/users', request as unknown as Record<string, unknown>);
+  }
+
+  static async getUser(id: string): Promise<AdminUser> {
+    return this.get<AdminUser>(`/users/${id}`);
+  }
+
+  static async updateUserStatus(id: string, request: UpdateUserStatusRequest): Promise<void> {
+    return this.put<void>(`/users/${id}/status`, request);
+  }
+
+  static async createUser(request: CreateUserRequest): Promise<AdminUser> {
+    return this.post<AdminUser>('/users', request);
+  }
+
+  static async deleteUser(id: string): Promise<void> {
+    return this.delete<void>(`/users/${id}`);
+  }
+}