refactor(storage): move file management routes from user to admin namespace

- Remove file list, stats, download, and deletion routes from '/api/v1/upload'
- Move these endpoints under '/api/v1/admin/uploads'
- Remove user-specific filtering from files query and statistics to aggregate system-wide uploads by default
- Allow admins to bypass ownership check when downloading private files
- Update backend unit tests, Swagger documentation, and frontend service client and components

frontend/components/layout/sidebar.tsx

@@ -71,8 +71,8 @@ const data = {
   ],
   admin: [
     { title: "用户管理", url: "/admin/users", icon: UserRound },
-    { title: "文件管理", url: "/admin/files", icon: FolderOpen },
     { title: "任务管理", url: "/admin/tasks", icon: Layers },
+    { title: "存储管理", url: "/admin/files", icon: FolderOpen },
     { title: "数据管理", url: "/admin/database", icon: Database },
     { title: "系统日志", url: "/admin/logs", icon: Terminal },
     { title: "系统配置", url: "/admin/system", icon: ShieldCheck },