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>

backend/app/routers/versions.py

@@ -2,6 +2,7 @@ from typing import Annotated, Any
 
 from fastapi import APIRouter, Depends, HTTPException, Request, status
 from sqlalchemy import select
+from starlette.requests import ClientDisconnect
 
 from app.deps import DB, CurrentUser, has_perm, require
 from app.models import GameVersion, Save, User
@@ -57,10 +58,13 @@ async def upload_version(
             async for chunk in request.stream():
                 f.write(chunk)
                 size += len(chunk)
-    except Exception:
+    except Exception as e:
         remove_upload(version.id)
         await db.delete(version)
         await db.commit()
+        if isinstance(e, ClientDisconnect):
+            # usually a proxy in front cut the body off (e.g. its own 413)
+            raise HTTPException(status.HTTP_400_BAD_REQUEST, "Загрузка прервана") from None
         raise
     if size == 0:
         remove_upload(version.id)