fix(auto setup): 修复初始测试连接硬编码问题导致使用自定义数据库测试失败无法执行 auto setup流程

backend/internal/setup/setup.go

@@ -164,8 +164,8 @@ func NeedsSetup() bool {
 func TestDatabaseConnection(cfg *DatabaseConfig) error {
 	// First, connect to the default 'postgres' database to check/create target database
 	defaultDSN := fmt.Sprintf(
-		"host=%s port=%d user=%s password=%s dbname=postgres sslmode=%s",
-		cfg.Host, cfg.Port, cfg.User, cfg.Password, cfg.SSLMode,
+		"host=%s port=%d user=%s password=%s dbname=%s sslmode=%s",
+		cfg.Host, cfg.Port, cfg.User, cfg.Password, cfg.DBName, cfg.SSLMode,
 	)
 
 	db, err := sql.Open("postgres", defaultDSN)