Initial commit: WYSIWYG Markdown Editor - Go backend + React/TypeScript frontend with Tailwind CSS

Backend:
- Cobra CLI with --data-dir, --port, --host flags
- Gin HTTP server with REST API for markdown CRUD operations
- File storage on disk (.md files only)
- Comprehensive logrus logging
- Backend tests with CRUD round-trip verification

Frontend:
- React 18 + TypeScript + Tailwind CSS
- Markdown editor with live GFM preview (react-markdown + remark-gfm)
- File management UI (list, create, open, save, delete)
- Theme switcher with Dark/Light/System modes
- Responsive design
- Frontend tests with vitest

Testing:
- All backend tests pass (go test ./...)
- All frontend tests pass (npm test)

cmd/main.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"markdown-editor/internal/server"
+	"markdown-editor/internal/logger"
+
+	"github.com/spf13/cobra"
+)
+
+var (
+	rootCmd = &cobra.Command{
+		Use:   "markdown-editor",
+		Short: "A markdown editor with preview",
+		Long:  "A markdown editor with preview - a WYSIWYG markdown editor server",
+		Run:   runServer,
+	}
+	dataDir string
+	port    int
+	host    string
+)
+
+func init() {
+	rootCmd.Flags().StringVar(&dataDir, "data-dir", "./data", "Storage path for markdown files")
+	rootCmd.Flags().IntVar(&port, "port", 8080, "Server port")
+	rootCmd.Flags().StringVar(&host, "host", "127.0.0.1", "Bind address")
+}
+
+func runServer(cmd *cobra.Command, args []string) {
+	log := logger.GetLogger()
+
+	log.Info("Starting Markdown Editor Server")
+	log.Infof("Data directory: %s", dataDir)
+	log.Infof("Port: %d", port)
+	log.Infof("Host: %s", host)
+
+	s := server.NewServer(dataDir, port, host)
+	
+	// Setup signal handling
+	sigChan := make(chan os.Signal, 1)
+	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)
+
+	go func() {
+		if err := s.Start(); err != nil {
+			log.Fatalf("Server error: %v", err)
+		}
+	}()
+
+	// Wait for signal
+	sig := <-sigChan
+	log.Infof("Received signal %v, shutting down...", sig)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	if err := s.Shutdown(ctx); err != nil {
+		log.Errorf("Shutdown error: %v", err)
+		os.Exit(1)
+	}
+	log.Info("Server stopped")
+}
+
+func Execute() error {
+	return rootCmd.Execute()
+}
+
+func main() {
+	if err := Execute(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+}