fix: move withdrawal commission deduction from application to approval

- commissionWithdrawLogic: remove upfront commission deduction;
  balance check now includes sum of all pending withdrawals to prevent
  double-spending; transaction only creates the withdrawal record (status=0)
- approveWithdrawal: add FOR UPDATE lock on user row, balance check before
  deducting, atomic commission decrement and commission log inside one
  transaction; clear user cache after commit
- rejectWithdrawal: remove commission refund and log — commission was never
  deducted on application under the new flow
- add migration 02150: refund commission for existing status=0 withdrawals
  that were deducted under the old logic; includes rollback script

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

pkg/xerr/errCode.go

@@ -37,6 +37,7 @@ const (
 	FamilyNotExist                uint32 = 20017
 	FamilyStatusInvalid           uint32 = 20018
 	FamilyOwnerOperationForbidden uint32 = 20019
+	WithdrawalStatusInvalid       uint32 = 20020
 )
 
 // Node error