Add standalone Go build alongside VSCode extension

Ports all five tools to a single 7.5 MB Windows exe with an embedded
WebView2 window, file-based config, single-instance focus, and clean
shutdown. Adds build.ps1 to build both targets from one command.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

standalone/single_instance.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func lockFilePath() string {
+	return filepath.Join(appDir(), ".hpltoolbox.lock")
+}
+
+// focusExistingInstance returns true if another instance was found and
+// successfully asked to focus its window. In that case the caller should exit.
+// Returns false if no live instance exists (and clears any stale lock).
+func focusExistingInstance() bool {
+	data, err := os.ReadFile(lockFilePath())
+	if err != nil {
+		return false
+	}
+	parts := strings.Split(strings.TrimSpace(string(data)), "\n")
+	if len(parts) != 2 {
+		_ = os.Remove(lockFilePath())
+		return false
+	}
+	pid, errPid := strconv.Atoi(strings.TrimSpace(parts[0]))
+	port, errPort := strconv.Atoi(strings.TrimSpace(parts[1]))
+	if errPid != nil || errPort != nil {
+		_ = os.Remove(lockFilePath())
+		return false
+	}
+
+	// Quick liveness check: PID must exist.
+	if proc, err := os.FindProcess(pid); err != nil || proc == nil {
+		_ = os.Remove(lockFilePath())
+		return false
+	}
+
+	// Ask the running instance to focus its window.
+	client := &http.Client{Timeout: 1500 * time.Millisecond}
+	url := fmt.Sprintf("http://127.0.0.1:%d/api/focus", port)
+	resp, err := client.Post(url, "application/json", bytes.NewReader(nil))
+	if err != nil {
+		// Lock file is stale (process died but didn't clean up).
+		_ = os.Remove(lockFilePath())
+		return false
+	}
+	_ = resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		_ = os.Remove(lockFilePath())
+		return false
+	}
+	return true
+}
+
+func writeLockFile(port int) error {
+	content := fmt.Sprintf("%d\n%d\n", os.Getpid(), port)
+	return os.WriteFile(lockFilePath(), []byte(content), 0644)
+}
+
+func removeLockFile() {
+	_ = os.Remove(lockFilePath())
+}