Route manual USDT/USDC convert through trading account (not funding).

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

backend/app/api/funds.py

@@ -167,11 +167,15 @@ async def funds_summary(_user: Annotated[str, Depends(require_user)]) -> dict[st
 async def funds_convert(
     body: ConvertBody, _user: Annotated[str, Depends(require_user)]
 ) -> dict[str, Any]:
+    """USDT↔USDC 市价兑换：一律在交易账户（对齐 OKX 现货 cash；SIM 同口径）。"""
     s = get_settings()
     rate = usdc_usdt_mid_rate()
     if s.is_sim:
         r = SimFundsWallets(get_db()).convert(
-            direction=body.direction, amount=float(body.amount), rate=rate
+            direction=body.direction,
+            amount=float(body.amount),
+            rate=rate,
+            account="trading",
         )
         if not r.get("ok"):
             raise HTTPException(status_code=400, detail=r.get("detail") or "兑换失败")
@@ -186,6 +190,12 @@ async def funds_convert(
         )
     finally:
         client.close()
+    try:
+        from ..strategy.open_capacity import invalidate_live_balance_cache
+
+        invalidate_live_balance_cache()
+    except Exception:
+        pass
     if not r.get("ok"):
         raise HTTPException(status_code=400, detail=r.get("detail") or "兑换失败")
     return r