feat(admin): add drag-and-drop group sort order

- Add `sort_order` field to groups table with migration
- Add `PUT /api/v1/admin/groups/sort-order` API for batch update
- Implement drag-and-drop UI using vue-draggable-plus
- All queries now order groups by sort_order
- Add i18n support (en/zh) for sort-related UI text
- Update test stubs to satisfy new interface methods

backend/internal/repository/api_key_repo.go

@@ -485,6 +485,7 @@ func groupEntityToService(g *dbent.Group) *service.Group {
 		ModelRoutingEnabled:             g.ModelRoutingEnabled,
 		MCPXMLInject:                    g.McpXMLInject,
 		SupportedModelScopes:            g.SupportedModelScopes,
+		SortOrder:                       g.SortOrder,
 		CreatedAt:                       g.CreatedAt,
 		UpdatedAt:                       g.UpdatedAt,
 	}

backend/internal/repository/group_repo.go

@@ -191,7 +191,7 @@ func (r *groupRepository) ListWithFilters(ctx context.Context, params pagination
 	groups, err := q.
 		Offset(params.Offset()).
 		Limit(params.Limit()).
-		Order(dbent.Asc(group.FieldID)).
+		Order(dbent.Asc(group.FieldSortOrder), dbent.Asc(group.FieldID)).
 		All(ctx)
 	if err != nil {
 		return nil, nil, err
@@ -218,7 +218,7 @@ func (r *groupRepository) ListWithFilters(ctx context.Context, params pagination
 func (r *groupRepository) ListActive(ctx context.Context) ([]service.Group, error) {
 	groups, err := r.client.Group.Query().
 		Where(group.StatusEQ(service.StatusActive)).
-		Order(dbent.Asc(group.FieldID)).
+		Order(dbent.Asc(group.FieldSortOrder), dbent.Asc(group.FieldID)).
 		All(ctx)
 	if err != nil {
 		return nil, err
@@ -245,7 +245,7 @@ func (r *groupRepository) ListActive(ctx context.Context) ([]service.Group, erro
 func (r *groupRepository) ListActiveByPlatform(ctx context.Context, platform string) ([]service.Group, error) {
 	groups, err := r.client.Group.Query().
 		Where(group.StatusEQ(service.StatusActive), group.PlatformEQ(platform)).
-		Order(dbent.Asc(group.FieldID)).
+		Order(dbent.Asc(group.FieldSortOrder), dbent.Asc(group.FieldID)).
 		All(ctx)
 	if err != nil {
 		return nil, err
@@ -497,3 +497,29 @@ func (r *groupRepository) BindAccountsToGroup(ctx context.Context, groupID int64
 
 	return nil
 }
+
+// UpdateSortOrders 批量更新分组排序
+func (r *groupRepository) UpdateSortOrders(ctx context.Context, updates []service.GroupSortOrderUpdate) error {
+	if len(updates) == 0 {
+		return nil
+	}
+
+	// 使用事务批量更新
+	tx, err := r.client.Tx(ctx)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = tx.Rollback() }()
+
+	for _, u := range updates {
+		if _, err := tx.Group.UpdateOneID(u.ID).SetSortOrder(u.SortOrder).Save(ctx); err != nil {
+			return translatePersistenceError(err, service.ErrGroupNotFound, nil)
+		}
+	}
+
+	if err := tx.Commit(); err != nil {
+		return err
+	}
+
+	return nil
+}