fix: Electron desktop app startup and add install script

- tryElectronApp() now finds the project directory via
  LAZY_UPDATE_MANAGER_DIR env, CWD, binary path, or $HOME
- Launches node_modules/.bin/electron directly instead of npm start
  (avoids recompiling the Go backend on every launch)
- Add install.sh with Electron fallback, desktop launcher, and
  prefer_electron config
- Desktop entry points to electron launcher for wofi support
- Update electron to v41.7.1

cmd/lazy-update-manager/main.go

@@ -288,20 +288,64 @@ func defaultConfigPath() string {
 }
 
 func tryElectronApp() error {
-	// Try to find and launch the Electron app
-	cmd := exec.Command("npm", "start")
+	projectDir := electronProjectDir()
+	if projectDir == "" {
+		return errors.New("LazyUpdateManager project directory not found – set LAZY_UPDATE_MANAGER_DIR or run from the project folder")
+	}
+
+	electronBin := filepath.Join(projectDir, "node_modules", ".bin", "electron")
+	if _, err := os.Stat(electronBin); err != nil {
+		electronBin = "electron"
+	}
+
+	cmd := exec.Command(electronBin, projectDir)
+	cmd.Dir = projectDir
 	cmd.Stdout = nil
 	cmd.Stderr = nil
 	cmd.Stdin = nil
-	if err := cmd.Run(); err != nil {
-		// Try electron directly
-		cmd = exec.Command("electron", ".")
-		cmd.Stdout = nil
-		cmd.Stderr = nil
-		cmd.Stdin = nil
-		return cmd.Run()
+	return cmd.Run()
+}
+
+func electronProjectDir() string {
+	if d := os.Getenv("LAZY_UPDATE_MANAGER_DIR"); d != "" {
+		if hasElectronMain(d) {
+			return d
+		}
 	}
-	return nil
+
+	if d, err := os.Getwd(); err == nil && hasElectronMain(d) {
+		return d
+	}
+
+	exe, err := os.Executable()
+	if err != nil {
+		return ""
+	}
+	exeDir := filepath.Dir(exe)
+
+	// binary in ~/Projekte/LazyUpdateManager/bin/
+	if p := filepath.Dir(exeDir); hasElectronMain(p) {
+		return p
+	}
+
+	// binary in ~/.local/bin/, project is at configured location
+	if p := filepath.Join(exeDir, "..", "Projekte", "LazyUpdateManager"); hasElectronMain(p) {
+		return p
+	}
+
+	// relative to $HOME
+	if home, err := os.UserHomeDir(); err == nil {
+		if p := filepath.Join(home, "Projekte", "LazyUpdateManager"); hasElectronMain(p) {
+			return p
+		}
+	}
+
+	return ""
+}
+
+func hasElectronMain(dir string) bool {
+	info, err := os.Stat(filepath.Join(dir, "electron", "main.cjs"))
+	return err == nil && !info.IsDir()
 }
 
 func usage() {