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)

internal/logger/logger.go

@@ -0,0 +1,32 @@
+package logger
+
+import (
+	"github.com/sirupsen/logrus"
+	"os"
+)
+
+var (
+	log *logrus.Logger
+)
+
+func init() {
+	log = logrus.New()
+	log.SetLevel(logrus.InfoLevel)
+	log.SetFormatter(&logrus.JSONFormatter{})
+
+	// Output to stderr by default
+	log.SetOutput(os.Stderr)
+}
+
+func GetLogger() *logrus.Logger {
+	return log
+}
+
+func SetLevel(level string) {
+	lvl, err := logrus.ParseLevel(level)
+	if err != nil {
+		log.Warnf("Invalid log level %s, using INFO", level)
+		return
+	}
+	log.SetLevel(lvl)
+}