feat(distribution): 补齐退款加价回退、本站自卖与开通默认规则

退款时压缩卖方加价，人工/自动批次仅完结单可入账，号主收入进主站钱包；仲裁后重算释放并支持作废未入账 DS。开通时四种模式按默认生效，对外口径合并为 35/40/25，不再单独展示通道费。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/router/router.go

@@ -667,6 +667,7 @@ func New(cfg config.Config, deps Dependencies, logger *zap.Logger) *gin.Engine {
 			adminRoutes.POST("/distribution/settlement-batches", requirePerm("distribution:settlement_manage"), distributionHandler.CreateSettlementBatch)
 			adminRoutes.GET("/distribution/settlement-batches/:id/items", requirePerm("distribution:settlement_view"), distributionHandler.ListSettlementItems)
 			adminRoutes.POST("/distribution/settlement-batches/:id/settle", requirePerm("distribution:settlement_manage"), distributionHandler.MarkSettlementBatch)
+			adminRoutes.POST("/distribution/settlement-batches/:id/cancel", requirePerm("distribution:settlement_manage"), distributionHandler.CancelSettlementBatch)
 			adminRoutes.GET("/files/object", fileHandler.Object)
 			adminRoutes.GET("/users", requirePerm("user:view"), adminUserHandler.List)
 			adminRoutes.POST("/users/:id/freeze", requirePerm("user:freeze"), adminUserHandler.Freeze)