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>

apis/public/user.api

@@ -109,8 +109,11 @@ type (
 		Rules []string `json:"rules" validate:"required"`
 	}
 	CommissionWithdrawRequest {
-		Amount  int64  `json:"amount"`
-		Content string `json:"content"`
+		Amount    int64  `json:"amount"`
+		Content   string `json:"content"`
+		Method    uint8  `json:"method" validate:"oneof=0 1 2 3"`
+		Account   string `json:"account,omitempty"`
+		QrCodeUrl string `json:"qr_code_url,omitempty"`
 	}
 	WithdrawalLog {
 		Id        int64  `json:"id"`
@@ -119,9 +122,15 @@ type (
 		Content   string `json:"content"`
 		Status    uint8  `json:"status"`
 		Reason    string `json:"reason,omitempty"`
+		Method    uint8  `json:"method"`
+		Account   string `json:"account"`
+		QrCodeUrl string `json:"qr_code_url"`
 		CreatedAt int64  `json:"created_at"`
 		UpdatedAt int64  `json:"updated_at"`
 	}
+	CancelWithdrawalRequest {
+		WithdrawalId int64 `json:"withdrawal_id" validate:"required,gt=0"`
+	}
 	QueryWithdrawalLogListRequest {
 		Page int `form:"page"`
 		Size int `form:"size"`
@@ -352,6 +361,10 @@ service ppanel {
 	@handler CommissionWithdraw
 	post /commission_withdraw (CommissionWithdrawRequest) returns (WithdrawalLog)
 
+	@doc "Cancel pending withdrawal"
+	@handler CancelWithdrawal
+	post /withdrawal_cancel (CancelWithdrawalRequest) returns (WithdrawalLog)
+
 	@doc "Query Withdrawal Log"
 	@handler QueryWithdrawalLog
 	get /withdrawal_log (QueryWithdrawalLogListRequest) returns (QueryWithdrawalLogListResponse)