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/group/node_group.go

@@ -0,0 +1,30 @@
+package group
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
+
+// NodeGroup 节点组模型
+type NodeGroup struct {
+	Id             int64     `gorm:"primaryKey"`
+	Name           string    `gorm:"type:varchar(255);not null;comment:Name"`
+	Description    string    `gorm:"type:varchar(500);comment:Description"`
+	Sort           int       `gorm:"default:0;index:idx_sort;comment:Sort Order"`
+	ForCalculation *bool     `gorm:"default:true;not null;comment:For Calculation: whether this node group participates in grouping calculation"`
+	MinTrafficGB   *int64    `gorm:"default:0;comment:Minimum Traffic (GB) for this node group"`
+	MaxTrafficGB   *int64    `gorm:"default:0;comment:Maximum Traffic (GB) for this node group"`
+	CreatedAt      time.Time `gorm:"<-:create;comment:Create Time"`
+	UpdatedAt      time.Time `gorm:"comment:Update Time"`
+}
+
+// TableName 指定表名
+func (*NodeGroup) TableName() string {
+	return "node_group"
+}
+
+// BeforeCreate GORM hook - 创建前回调
+func (ng *NodeGroup) BeforeCreate(tx *gorm.DB) error {
+	return nil
+}