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/model/user/user.go

@@ -167,8 +167,11 @@ type Withdrawal struct {
 	UserId    int64     `gorm:"index:idx_user_id;not null;comment:User ID"`
 	Amount    int64     `gorm:"not null;comment:Withdrawal Amount"`
 	Content   string    `gorm:"type:text;comment:Withdrawal Content"`
-	Status    uint8     `gorm:"type:tinyint(1);default:0;comment:Withdrawal Status: 0: Pending 1: Approved 2: Rejected"`
+	Status    uint8     `gorm:"type:tinyint(1);default:0;comment:Withdrawal Status: 0: Pending 1: Approved 2: Rejected 3: Cancelled"`
 	Reason    string    `gorm:"type:varchar(500);default:'';comment:Rejection Reason"`
+	Method    uint8     `gorm:"type:tinyint(1);default:0;comment:收款方式 0:其他 1:支付宝 2:微信 3:银行卡"`
+	Account   string    `gorm:"type:varchar(255);default:'';comment:收款账号"`
+	QrCodeUrl string    `gorm:"type:varchar(500);default:'';comment:收款码图片URL"`
 	CreatedAt time.Time `gorm:"<-:create;comment:Creation Time"`
 	UpdatedAt time.Time `gorm:"comment:Update Time"`
 }