feat: implement withdrawal improvements P01-P05

- P04: fix Withdrawal.TableName() to return 'withdrawals'
- P03: add WithdrawalStatus* and WithdrawalMethod* constants; replace magic numbers; add CommissionTypeWithdrawCancel=338
- P01: add POST /v1/public/user/withdrawal_cancel to cancel pending withdrawals with ownership check, row lock, commission refund, and audit log
- P02: add method/account/qr_code_url fields to Withdrawal model and API; add input validation (qr_code_url required for Alipay/Wechat, account required for bank)
- P05: add method filter to admin GET /v1/admin/user/withdrawal/list

Co-authored-by: multica-agent <github@multica.ai>

internal/logic/admin/user/withdrawalCommon.go

@@ -25,9 +25,9 @@ func approveWithdrawal(ctx context.Context, svcCtx *svc.ServiceContext, withdraw
 		}
 
 		if err := tx.Model(&usermodel.Withdrawal{}).
-			Where("id = ? AND status = 0", withdrawalID).
+			Where("id = ? AND status = ?", withdrawalID, usermodel.WithdrawalStatusPending).
 			Updates(map[string]interface{}{
-				"status": 1,
+				"status": usermodel.WithdrawalStatusApproved,
 				"reason": "",
 			}).Error; err != nil {
 			return errors.Wrapf(xerr.NewErrCode(xerr.DatabaseUpdateError), "approve withdrawal failed: %v", err)
@@ -52,9 +52,9 @@ func rejectWithdrawal(ctx context.Context, svcCtx *svc.ServiceContext, withdrawa
 		}
 
 		if err := tx.Model(&usermodel.Withdrawal{}).
-			Where("id = ? AND status = 0", withdrawalID).
+			Where("id = ? AND status = ?", withdrawalID, usermodel.WithdrawalStatusPending).
 			Updates(map[string]interface{}{
-				"status": 2,
+				"status": usermodel.WithdrawalStatusRejected,
 				"reason": reason,
 			}).Error; err != nil {
 			return errors.Wrapf(xerr.NewErrCode(xerr.DatabaseUpdateError), "reject withdrawal failed: %v", err)