fix: flush log file, show last lines in error output

internal/native/native.go

@@ -146,11 +146,23 @@ http {
 	if err == nil {
 		setupCmd.Stdout = logFile
 		setupCmd.Stderr = logFile
-		defer logFile.Close()
 	}
-
-	if err := setupCmd.Run(); err != nil {
-		return fmt.Errorf("installation failed — check %s/install.log: %w", workDir, err)
+	runErr := setupCmd.Run()
+	if logFile != nil {
+		logFile.Close()
+	}
+	if runErr != nil {
+		// Read the log for the error message
+		if data, err := os.ReadFile(filepath.Join(workDir, "install.log")); err == nil && len(data) > 0 {
+			lines := strings.Split(string(data), "\n")
+			// Print last few lines as the error
+			start := len(lines) - 5
+			if start < 0 {
+				start = 0
+			}
+			return fmt.Errorf("%s", strings.Join(lines[start:], "\n"))
+		}
+		return fmt.Errorf("installation failed (exit %v) — check %s/install.log", runErr, workDir)
 	}
 
 	// 6. Enable and start systemd service