Add admin maintenance endpoints and file deletion functionality

- Introduced a new `/api/admin/maintenance` route for administrative maintenance tasks, requiring admin authorization.
- Implemented the `DeleteAsync` method in `IFileStorage` to allow for the deletion of files associated with closed support tickets.
- Updated API documentation to include details about the new maintenance operations and their effects on closed tickets.
- Enhanced frontend routing to include the new maintenance section in the admin panel, improving navigation for administrators.
- Added localization support for maintenance-related actions in both Russian and English.

frontend/src/shared/api/types.ts

@@ -270,6 +270,10 @@ export type TicketSummaryDto = {
   messagePreview: string | null
 }
 
+export type DeleteClosedTicketsResponseDto = {
+  deletedCount: number
+}
+
 export type TicketDetailDto = {
   id: string
   userId: string