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_test.go

@@ -0,0 +1,35 @@
+package logger
+
+import (
+	"testing"
+
+	"github.com/sirupsen/logrus"
+)
+
+func TestGetLogger(t *testing.T) {
+	log := GetLogger()
+	if log == nil {
+		t.Error("Logger is nil")
+	}
+}
+
+func TestSetLevel(t *testing.T) {
+	// Test valid levels
+	SetLevel("debug")
+	SetLevel("info")
+	SetLevel("warn")
+	SetLevel("error")
+
+	// Test invalid level (should not panic)
+	SetLevel("invalid")
+}
+
+func TestJSONFormatter(t *testing.T) {
+	log := GetLogger()
+	log.SetFormatter(&logrus.JSONFormatter{})
+	
+	// Just verify the formatter doesn't panic
+	if log.Formatter == nil {
+		t.Error("Formatter is nil")
+	}
+}