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/internal/logging/logger.go

@@ -0,0 +1,37 @@
+package logging
+
+import (
+	"net/http"
+	"time"
+
+	"github.com/sirupsen/logrus"
+)
+
+var Logger *logrus.Logger
+
+// Init initializes the logger
+func Init() {
+	Logger = logrus.New()
+	Logger.SetFormatter(&logrus.JSONFormatter{})
+	Logger.SetLevel(logrus.InfoLevel)
+}
+
+// RequestMiddleware logs HTTP requests
+func RequestMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+		
+		Logger.WithFields(logrus.Fields{
+			"method": r.Method,
+			"path":   r.URL.Path,
+		}).Info("Request started")
+		
+		next.ServeHTTP(w, r)
+		
+		Logger.WithFields(logrus.Fields{
+			"method": r.Method,
+			"path":   r.URL.Path,
+			"duration": time.Since(start).String(),
+		}).Info("Request completed")
+	})
+}