feat: implement WYSIWYG markdown editor

Add complete markdown editor with Go backend and React/TypeScript frontend.

Backend:
- Cobra CLI with configurable host, port, data-dir, static-dir flags
- REST API for CRUD operations on markdown files (GET, POST, PUT, DELETE)
- File storage with flat .md structure
- Comprehensive Logrus logging for all operations
- Static asset serving for frontend

Frontend:
- React 18 + TypeScript + Tailwind CSS
- Live markdown editor with GFM preview (react-markdown)
- File management UI (list, create, open, save, delete)
- Theme system (Light/Dark/System) with localStorage persistence
- Responsive design (320px - 1920px+)

Testing:
- 6 backend tests covering CRUD round-trip, validation, error handling
- 19 frontend tests covering API, theme system, and UI components
- All tests passing with single 'make test' command

Build:
- Frontend compiles to optimized assets in dist/
- Backend can serve frontend via --static-dir flag

backend/cmd/server/root.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+
+	"github.com/evanreichard/markdown-editor/internal/api"
+	"github.com/evanreichard/markdown-editor/internal/config"
+	"github.com/evanreichard/markdown-editor/internal/logging"
+	"github.com/evanreichard/markdown-editor/internal/router"
+	"github.com/evanreichard/markdown-editor/internal/storage"
+	"github.com/spf13/cobra"
+)
+
+var (
+	dataDir  string
+	port     string
+	host     string
+	staticDir string
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "server",
+	Short: "Markdown editor server",
+	Long:  "A markdown editor server with REST API and frontend support",
+	Run:   runServer,
+}
+
+func init() {
+	rootCmd.Flags().StringVar(&dataDir, "data-dir", "./data", "Storage path for markdown files")
+	rootCmd.Flags().StringVar(&port, "port", "8080", "Server port")
+	rootCmd.Flags().StringVar(&host, "host", "127.0.0.1", "Bind address")
+	rootCmd.Flags().StringVar(&staticDir, "static-dir", "./frontend/dist", "Path to static assets")
+}
+
+func runServer(cmd *cobra.Command, args []string) {
+	cfg := &config.Config{
+		DataDir: dataDir,
+		Port:    port,
+		Host:    host,
+	}
+
+	logging.Init()
+	logging.Logger.WithFields(map[string]interface{}{
+		"data_dir":   cfg.DataDir,
+		"host":       cfg.Host,
+		"port":       cfg.Port,
+		"static_dir": staticDir,
+	}).Info("Starting markdown editor server")
+
+	// Initialize storage
+	store, err := storage.New(cfg.DataDir)
+	if err != nil {
+		logging.Logger.WithError(err).Fatal("Failed to initialize storage")
+	}
+
+	// Initialize handlers
+	handlers := api.New(store)
+
+	// Create router
+	mux := router.New(handlers, staticDir)
+
+	// Wrap with logging middleware
+	handler := logging.RequestMiddleware(mux)
+
+	// Start server
+	addr := cfg.Addr()
+	logging.Logger.WithField("addr", addr).Info("Server listening")
+	if err := http.ListenAndServe(addr, handler); err != nil {
+		logging.Logger.WithError(err).Fatal("Server error")
+	}
+}
+
+func main() {
+	if err := rootCmd.Execute(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+}