perf(chat): 优化后台客服会话查询与状态

backend/internal/modules/chat/conversation_test.go

@@ -24,6 +24,7 @@ func setupConversationTestDB(t *testing.T) *gorm.DB {
 		&model.RentalOrder{},
 		&model.ChatConversation{},
 		&model.ChatParticipant{},
+		&model.ChatAdminConversationState{},
 		&model.ChatMessage{},
 	); err != nil {
 		t.Fatalf("数据库迁移失败: %v", err)