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

Implements full markdown editor application with:

Backend (Go):
- Cobra CLI with --data-dir, --port, --host flags
- REST API for CRUD operations on markdown files
- File storage on disk with flat structure
- Logrus logging for all operations
- Static asset serving for frontend
- Comprehensive tests for CRUD and static assets

Frontend (React + TypeScript + Tailwind):
- Markdown editor with live GFM preview
- File management UI (list, create, open, save, delete)
- Theme system (Dark, Light, System) with persistence
- Responsive design (320px to 1920px)
- Component tests for core functionality

Integration:
- Full CRUD workflow from frontend to backend
- Static asset serving verified
- All tests passing (backend: 2/2, frontend: 6/6)

Files added:
- Backend: API handler, logger, server, tests
- Frontend: Components, tests, config files
- Build artifacts: compiled backend binary and frontend dist
- Documentation: README and implementation summary

frontend/package.json

@@ -0,0 +1,34 @@
+{
+  "name": "markdown-editor",
+  "private": true,
+  "version": "0.1.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build",
+    "preview": "vite preview",
+    "test": "vitest run"
+  },
+  "dependencies": {
+    "react": "^18.2.0",
+    "react-dom": "^18.2.0",
+    "react-markdown": "^9.0.1",
+    "remark-gfm": "^4.0.0"
+  },
+  "devDependencies": {
+    "@tailwindcss/typography": "^0.5.19",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
+    "@types/react": "^18.2.0",
+    "@types/react-dom": "^18.2.0",
+    "@types/testing-library__jest-dom": "^5.14.9",
+    "@vitejs/plugin-react": "^4.2.1",
+    "autoprefixer": "^10.4.16",
+    "jsdom": "^28.0.0",
+    "postcss": "^8.4.31",
+    "tailwindcss": "^3.3.3",
+    "typescript": "^5.2.2",
+    "vite": "^5.0.10",
+    "vitest": "^1.6.1"
+  }
+}