Upload: clearer proxy 413 error, clean up after interrupted uploads

- Show a readable message when a reverse proxy rejects the archive with 413
- Delete the freshly created game if its archive upload fails
- Turn ClientDisconnect during upload into a short 400 instead of a traceback

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/api.ts

@@ -98,7 +98,9 @@ export function uploadRaw<T>(method: string, url: string, file: Blob,
         /* empty */
       }
       if (xhr.status >= 200 && xhr.status < 300) resolve(data);
-      else reject(new ApiError(xhr.status, data?.detail ?? xhr.statusText));
+      else if (xhr.status === 413 && !data?.detail)
+        reject(new ApiError(413, "Файл слишком большой для прокси перед сервером (client_max_body_size)"));
+      else reject(new ApiError(xhr.status, data?.detail ?? (xhr.statusText || `Ошибка ${xhr.status}`)));
     };
     xhr.onerror = () => reject(new ApiError(0, "Сетевая ошибка"));
     xhr.send(file);