Features:

- Node group CRUD operations with traffic-based filtering
  - Three grouping modes: average distribution, subscription-based, and traffic-based
  - Automatic and manual group recalculation with history tracking
  - Group assignment preview before applying changes
  - User subscription group locking to prevent automatic reassignment
  - Subscribe-to-group mapping configuration
  - Group calculation history and detailed reports
  - System configuration for group management (enabled/mode/auto_create)

  Database:
  - Add node_group table for group definitions
  - Add group_history and group_history_detail tables for tracking
  - Add node_group_ids (JSON) to nodes and subscribe tables
  - Add node_group_id and group_locked fields to user_subscribe table
  - Add migration files for schema changes

internal/model/user/model.go

@@ -27,6 +27,7 @@ type SubscribeDetails struct {
 	OrderId     int64                `gorm:"index:idx_order_id;not null;comment:Order ID"`
 	SubscribeId int64                `gorm:"index:idx_subscribe_id;not null;comment:Subscription ID"`
 	Subscribe   *subscribe.Subscribe `gorm:"foreignKey:SubscribeId;references:Id"`
+	NodeGroupId int64                `gorm:"index:idx_node_group_id;not null;default:0;comment:Node Group ID (single ID)"`
 	StartTime   time.Time            `gorm:"default:CURRENT_TIMESTAMP(3);not null;comment:Subscription Start Time"`
 	ExpireTime  time.Time            `gorm:"default:NULL;comment:Subscription Expire Time"`
 	FinishedAt  *time.Time           `gorm:"default:NULL;comment:Finished Time"`