feat: 新增 MySQL 数据库驱动支持，支持跨设备数据同步

backend/tests/config/config_test.go

@@ -158,7 +158,10 @@ func TestSaveAndLoadConfig(t *testing.T) {
 			WriteTimeout: 45 * time.Second,
 		},
 		Database: config.DatabaseConfig{
+			Driver:          "sqlite",
 			Path:            filepath.Join(tmpDir, "test.db"),
+			Port:            3306,
+			DBName:          "nex",
 			MaxIdleConns:    15,
 			MaxOpenConns:    150,
 			ConnMaxLifetime: 2 * time.Hour,