Add option close liquidity gate with 30% bid/mark cap.

Block new opens while flat legs wait; emergency close bypasses the check.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/api/sim.py

@@ -37,6 +37,8 @@ async def sim_open_group(
     _user: Annotated[str, Depends(require_user)],
     body: ManualOpenBody | None = None,
 ) -> dict:
+    if Matcher().has_open_position():
+        raise HTTPException(status_code=409, detail="有未平仓，禁止开下一组")
     gw = get_gateway()
     pick = await gw.pick_for_open_async()
     if pick is None: