refactor: unify into single muyue binary with embedded desktop mode

- Merge muyue + muyue-desktop into one binary (13MB)
- `muyue` starts TUI, `muyue desktop` launches web UI in browser
- Move frontend from cmd/muyue-desktop/frontend/ to web/ (standard Go layout)
- Add web/embed.go with //go:embed all:dist for frontend assets
- Add internal/desktop/ package (server, browser open, SPA routing, signals)
- Split internal/api/api.go into server.go + handlers.go
- Add internal/desktop/desktop.go with SPA fallback and --port/--no-open flags
- Clean package.json: remove unused @xterm/xterm, switch to ESM
- Fix vite.config.js proxy to use port 8095 for dev mode
- Add Makefile targets: frontend, desktop, dev-desktop
- Update all CI workflows: single binary build, web/ paths
- Remove cmd/muyue-desktop/ entirely

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

internal/desktop/desktop.go

@@ -0,0 +1,131 @@
+package desktop
+
+import (
+	"fmt"
+	"io/fs"
+	"log"
+	"net"
+	"net/http"
+	"os"
+	"os/exec"
+	"os/signal"
+	"strconv"
+	"strings"
+	"syscall"
+
+	"github.com/muyue/muyue/internal/api"
+	"github.com/muyue/muyue/internal/config"
+	"github.com/muyue/muyue/internal/version"
+	"github.com/muyue/muyue/web"
+)
+
+type options struct {
+	port   int
+	noOpen bool
+}
+
+type option func(*options)
+
+func WithPort(port int) option {
+	return func(o *options) { o.port = port }
+}
+
+func WithNoOpen(noOpen bool) option {
+	return func(o *options) { o.noOpen = noOpen }
+}
+
+func parseFlags(args []string) []option {
+	var opts []option
+	for _, arg := range args {
+		switch {
+		case arg == "--no-open":
+			opts = append(opts, WithNoOpen(true))
+		case strings.HasPrefix(arg, "--port="):
+			if p, err := strconv.Atoi(strings.TrimPrefix(arg, "--port=")); err == nil {
+				opts = append(opts, WithPort(p))
+			}
+		case arg == "--port":
+			// handled as prefix case
+		}
+	}
+	return opts
+}
+
+func Run(cfg *config.MuyueConfig, args []string) error {
+	o := options{}
+	for _, opt := range parseFlags(args) {
+		opt(&o)
+	}
+
+	log.Printf("%s Desktop v%s", version.Name, version.Version)
+
+	srv := api.NewServer(cfg)
+
+	frontendFS, err := fs.Sub(web.Assets, "dist")
+	if err != nil {
+		return fmt.Errorf("frontend assets: %w", err)
+	}
+
+	mux := http.NewServeMux()
+	mux.Handle("/api/", srv)
+	mux.Handle("/", spaHandler(http.FileServer(http.FS(frontendFS))))
+
+	addr := fmt.Sprintf("127.0.0.1:%d", o.port)
+	listener, err := net.Listen("tcp", addr)
+	if err != nil {
+		return fmt.Errorf("bind %s: %w", addr, err)
+	}
+	port := listener.Addr().(*net.TCPAddr).Port
+
+	go func() {
+		if err := http.Serve(listener, mux); err != nil {
+			log.Fatalf("Server error: %v", err)
+		}
+	}()
+
+	url := fmt.Sprintf("http://127.0.0.1:%d", port)
+	log.Printf("Listening on %s", url)
+
+	if !o.noOpen {
+		openBrowser(url)
+		log.Printf("Opened browser")
+	}
+
+	quit := make(chan os.Signal, 1)
+	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
+	<-quit
+
+	log.Println("Shutting down...")
+	return nil
+}
+
+func spaHandler(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		path := r.URL.Path
+		if path != "/" && !strings.Contains(path, ".") {
+			r.URL.Path = "/"
+		}
+		next.ServeHTTP(w, r)
+	})
+}
+
+func openBrowser(url string) {
+	var cmd *exec.Cmd
+	switch {
+	case exists("xdg-open"):
+		cmd = exec.Command("xdg-open", url)
+	case exists("open"):
+		cmd = exec.Command("open", url)
+	case exists("cmd"):
+		cmd = exec.Command("cmd", "/c", "start", url)
+	default:
+		fmt.Printf("Open manually: %s\n", url)
+		return
+	}
+	_ = cmd.Start()
+}
+
+func exists(name string) bool {
+	_, err := exec.LookPath(name)
+	return err == nil
+}