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>

initialize/migrate/database/02123_withdrawal_method.down.sql

@@ -0,0 +1,4 @@
+ALTER TABLE `withdrawals`
+  DROP COLUMN `qr_code_url`,
+  DROP COLUMN `account`,
+  DROP COLUMN `method`;

initialize/migrate/database/02123_withdrawal_method.up.sql

@@ -0,0 +1,4 @@
+ALTER TABLE `withdrawals`
+  ADD COLUMN `method`      TINYINT(1)   NOT NULL DEFAULT 0 COMMENT '收款方式 0:其他 1:支付宝 2:微信 3:银行卡' AFTER `content`,
+  ADD COLUMN `account`     VARCHAR(255) NOT NULL DEFAULT '' COMMENT '收款账号' AFTER `method`,
+  ADD COLUMN `qr_code_url` VARCHAR(500) NOT NULL DEFAULT '' COMMENT '收款码图片URL' AFTER `account`;