Normalize TRANSFER_CCY to uppercase so Gate wallet transfers do not fail.

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

lib/exchange/gate_transfer_lib.py

@@ -22,6 +22,7 @@ def execute_transfer_usdt(
 ) -> tuple[bool, str, Any]:
     if amount <= 0:
         return False, "划转金额必须大于0", None
+    ccy = (transfer_ccy or "USDT").strip().upper() or "USDT"
     ok_live, reason = ensure_live_ready()
     if not ok_live:
         return False, reason, None
@@ -31,7 +32,7 @@ def execute_transfer_usdt(
         except Exception:
             pass
     try:
-        resp = exchange.transfer(transfer_ccy, float(amount), from_account, to_account)
+        resp = exchange.transfer(ccy, float(amount), from_account, to_account)
         return True, "划转成功", resp
     except Exception as e:
         msg = str(e)