Add maintenance management features: implement maintenance endpoints in the API, enhance media upload handling to skip duplicate files, and update frontend routes and translations for maintenance operations.

backend/src/TeleWave.Api/Program.cs

@@ -116,6 +116,7 @@ app.MapMediaEndpoints();
 app.MapShowEndpoints();
 app.MapChannelEndpoints();
 app.MapStreamingEndpoints();
+app.MapMaintenanceEndpoints();
 
 // Раздача статики SPA из wwwroot + fallback на index.html для клиентских маршрутов.
 app.UseDefaultFiles();