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

apis/admin/user.api

@@ -78,6 +78,8 @@ type (
 		OrderId     int64     `json:"order_id"`
 		SubscribeId int64     `json:"subscribe_id"`
 		Subscribe   Subscribe `json:"subscribe"`
+		NodeGroupId int64     `json:"node_group_id"`
+		GroupLocked bool      `json:"group_locked"`
 		StartTime   int64     `json:"start_time"`
 		ExpireTime  int64     `json:"expire_time"`
 		ResetTime   int64     `json:"reset_time"`