fix: second-pass review bugs in server and core

- ExportRunner: stop batch on first error (was continuing, overwriting
  error status with done)
- Export route: validate input_path against MEDIA_DIRS
- Export route: validate encoder, portrait_ratio, folder_suffix, name
- Export route: fix format check for WebP sequence
- Export route: add _ separator in folder_suffix (match GUI)
- Export route: use realpath consistently in delete endpoint
- Export route: drop runner ref on completion (prevent memory leak)
- ProcessedDB: use cursor-level row_factory (thread-safe)
- WebSocket: catch all exceptions in connect, cleanup in finally
- Dockerfile: use uvicorn[standard] for websockets support

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/ws.py

@@ -18,7 +18,9 @@ async def connect(ws: WebSocket):
     try:
         while True:
             await ws.receive_text()  # keep alive
-    except WebSocketDisconnect:
+    except (WebSocketDisconnect, Exception):
+        pass
+    finally:
         with _lock:
             if ws in _connections:
                 _connections.remove(ws)