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/log/log.go

@@ -50,6 +50,7 @@ const (
 	CommissionTypeAdjust         uint16 = 335 // Admin Adjust
 	CommissionTypeConvertBalance uint16 = 336 // Convert to Balance
 	CommissionTypeWithdrawReject uint16 = 337 // Withdraw rejected refund
+	CommissionTypeWithdrawCancel uint16 = 338 // 用户取消提现退佣金
 	GiftTypeIncrease             uint16 = 341 // Increase
 	GiftTypeReduce               uint16 = 342 // Reduce
 )