gui: add Wails v3 desktop app skeleton

- Go upgraded to 1.25.10 (required by Wails v3)
- Wails v3 installed (alpha.96)
- Frontend: Svelte+Vite scaffold in frontend/
- guimain.go: Wails GUI entry point (compiled with -tags gui)
- wails_service.go: stub service for Wails bindings
- Verstak desktop binary builds: go build -tags gui -o verstak-gui .
- CLI (./cmd/verstak/) unaffected
- Legacy HTTP GUI (internal/gui/) preserved as prototype
- Build: 24MB ELF binary with GTK4/WebKit2GTK-6

Build commands:
  CLI:  go build -o verstak ./cmd/verstak/
  GUI:  cd frontend && npm run build && go build -tags gui -o verstak-gui .

cmd/verstak-gui/main.go

@@ -1,71 +0,0 @@
-//go:build gui
-// +build gui
-
-package main
-
-import (
-	"fmt"
-	"log"
-	"os"
-	"os/exec"
-	"os/signal"
-	"path/filepath"
-	"runtime"
-	"syscall"
-
-	gui "verstak/internal/gui"
-	"verstak/internal/core/storage"
-)
-
-func main() {
-	vaultPath := "."
-	if len(os.Args) > 1 {
-		vaultPath = os.Args[1]
-	}
-
-	abs, err := filepath.Abs(vaultPath)
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	dbPath := filepath.Join(abs, ".verstak", "index.db")
-	db, err := storage.Open(dbPath)
-	if err != nil {
-		log.Fatalf("Open vault: %v", err)
-	}
-	defer db.Close()
-
-	srv := gui.NewServer(db, abs)
-	addr, err := srv.Start()
-	if err != nil {
-		log.Fatalf("Start GUI: %v", err)
-	}
-
-	fmt.Println("Верстак GUI:", addr)
-	openBrowser(addr)
-
-	// Wait for interrupt.
-	sig := make(chan os.Signal, 1)
-	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
-	<-sig
-
-	srv.Stop()
-	deferFunc()
-}
-
-func openBrowser(url string) {
-	var cmd *exec.Cmd
-	switch runtime.GOOS {
-	case "linux":
-		cmd = exec.Command("xdg-open", url)
-	case "darwin":
-		cmd = exec.Command("open", url)
-	case "windows":
-		cmd = exec.Command("cmd", "/c", "start", "", url)
-	}
-	if cmd != nil {
-		go cmd.Start()
-	}
-}
-
-func deferFunc() {}