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/model.go

@@ -0,0 +1,14 @@
+package group
+
+import (
+	"gorm.io/gorm"
+)
+
+// AutoMigrate 自动迁移数据库表
+func AutoMigrate(db *gorm.DB) error {
+	return db.AutoMigrate(
+		&NodeGroup{},
+		&GroupHistory{},
+		&GroupHistoryDetail{},
+	)
+}