fix(wallet): enforce consistent withdrawal accounting

backend/api/internal/models/wallet_apply_cash.go

@@ -25,6 +25,7 @@ type WalletApplyCash struct {
 	ReviewedAt       *time.Time `gorm:"column:reviewed_at;type:timestamptz" json:"reviewed_at"`                                                                       // 审核时间
 	ReviewReason     string     `gorm:"column:review_reason;type:text;not null;default:''" json:"review_reason"`                                                      // 审核原因
 	CompletedAt      *time.Time `gorm:"column:completed_at;type:timestamptz" json:"completed_at"`                                                                     // 完成时间
+	BalanceReserved  bool       `gorm:"column:balance_reserved;not null;default:false;index" json:"balance_reserved"`                                                 // 是否已在申请时同时预扣总余额和可提现余额
 }
 
 func init()                                      { database.AppendMigrate(&WalletApplyCash{}) }