feat: implement WYSIWYG markdown editor with Go backend and React frontend

- Backend: Go HTTP server with Cobra CLI (--data-dir, --port, --host flags)
- CRUD REST API for markdown files with JSON error responses
- File storage in flat directory structure (flat structure, .md files only)
- Comprehensive logrus logging for all operations
- Static file serving for frontend build (./frontend/dist)
- Frontend: React + TypeScript + Tailwind CSS
- Markdown editor with live GFM preview
- File management: list, create, open, save, delete
- Theme system (Dark, Light, System) with persistence
- Responsive design for desktop and mobile
- Backend tests (storage, API handlers) and frontend tests

cmd/root.go

@@ -0,0 +1,100 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"eval/internal/api"
+	"eval/internal/config"
+	"eval/internal/storage"
+	"github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+)
+
+var (
+	cfg = config.NewConfig()
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "eval",
+	Short: "WYSIWYG Markdown Editor Server",
+	Long:  `Eval is a markdown editor with preview featuring Go backend and React frontend.`,
+	Run: func(cmd *cobra.Command, args []string) {
+		runServer(cmd)
+	},
+}
+
+func init() {
+	cfg.AddFlags(rootCmd)
+	rootCmd.PersistentFlags().String("log-level", "info", "Log level (debug, info, warn, error)")
+}
+
+func runServer(cmd *cobra.Command) {
+	// Initialize logger
+	logger := logrus.New()
+	logger.SetFormatter(&logrus.TextFormatter{
+		FullTimestamp: true,
+	})
+	logLevel, _ := cmd.Flags().GetString("log-level")
+	if logLevel != "" {
+		level, err := logrus.ParseLevel(logLevel)
+		if err != nil {
+			logger.Warnf("invalid log level: %v, using info", err)
+			level = logrus.InfoLevel
+		}
+		logger.SetLevel(level)
+	}
+
+	// Validate config
+	if err := cfg.Validate(); err != nil {
+		logger.Fatalf("invalid configuration: %v", err)
+	}
+
+	// Ensure data directory exists
+	if err := cfg.EnsureDataDir(); err != nil {
+		logger.Fatalf("failed to create data directory: %v", err)
+	}
+	logger.Infof("using data directory: %s", cfg.DataDirPath())
+
+	// Initialize storage
+	store := storage.NewStorage(cfg.DataDirPath())
+
+	// Initialize API handlers
+	handlers := api.NewHandlers(store, cfg, logger)
+
+	// Determine build directory (check both build and dist)
+	buildDir := "./frontend/build"
+	distDir := "./frontend/dist"
+	
+	if _, err := os.Stat(buildDir); os.IsNotExist(err) {
+		if _, err := os.Stat(distDir); err == nil {
+			buildDir = distDir
+		}
+	}
+	
+	if rel, err := filepath.Rel(cfg.DataDirPath(), buildDir); err == nil {
+		buildDir = rel
+	}
+	logger.Infof("serving static files from: %s", buildDir)
+
+	// Setup routes
+	router, err := handlers.SetupRoutes(buildDir)
+	if err != nil {
+		logger.Fatalf("failed to setup routes: %v", err)
+	}
+
+	// Start server
+	if err := handlers.StartServer(router); err != nil {
+		logger.Fatalf("server error: %v", err)
+	}
+}
+
+// Execute starts the root command
+// This is called from main.go in the main package
+func Execute() {
+	if err := rootCmd.Execute(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}