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/upload/admin-upload.service.ts

@@ -0,0 +1,40 @@
+import type {InternalAxiosRequestConfig} from 'axios';
+
+import {BaseService} from '../core/base.service';
+import type {FileStatsResponse, ListUploadsResponse} from './types';
+
+export class AdminUploadService extends BaseService {
+  protected static readonly basePath = '/api/v1/admin/uploads';
+
+  static async listUploads(
+    page = 1,
+    pageSize = 20,
+    keyword?: string,
+    type?: string,
+    extension?: string,
+  ): Promise<ListUploadsResponse> {
+    const params: Record<string, string | number> = { page, page_size: pageSize };
+    if (keyword) params.keyword = keyword;
+    if (type) params.type = type;
+    if (extension) params.extension = extension;
+    return this.get<ListUploadsResponse>('', params);
+  }
+
+  static async getFileStats(): Promise<FileStatsResponse> {
+    return this.get<FileStatsResponse>('/stats');
+  }
+
+  static async deleteFile(id: string): Promise<void> {
+    return this.delete<void>(`/${id}`);
+  }
+
+  static getDownloadUrl(id: string): string {
+    return `${this.basePath}/download/${id}`;
+  }
+
+  static async batchDownload(ids: string[]): Promise<Blob> {
+    return this.post<Blob>('/download/batch', { ids }, {
+      responseType: 'blob',
+    } as InternalAxiosRequestConfig);
+  }
+}