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

frontend/package.json

@@ -0,0 +1,40 @@
+{
+  "name": "markdown-editor-frontend",
+  "version": "1.0.0",
+  "description": "Markdown editor with live preview",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc && vite build",
+    "preview": "vite preview",
+    "test": "vitest",
+    "lint": "eslint src --ext ts,tsx"
+  },
+  "dependencies": {
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1",
+    "react-markdown": "^9.0.1",
+    "remark-gfm": "^4.0.0",
+    "lucide-react": "^0.263.1"
+  },
+  "devDependencies": {
+    "@types/react": "^18.3.1",
+    "@types/react-dom": "^18.3.0",
+    "@typescript-eslint/eslint-plugin": "^7.0.0",
+    "@typescript-eslint/parser": "^7.0.0",
+    "@vitejs/plugin-react": "^4.3.0",
+    "autoprefixer": "^10.4.19",
+    "eslint": "^8.57.0",
+    "eslint-plugin-react-hooks": "^4.6.0",
+    "eslint-plugin-react-refresh": "^0.4.6",
+    "postcss": "^8.4.38",
+    "tailwindcss": "^3.4.3",
+    "typescript": "^5.4.5",
+    "vite": "^5.2.8",
+    "vitest": "^1.5.0",
+    "jsdom": "^24.0.0",
+    "@testing-library/react": "^15.0.6",
+    "@testing-library/jest-dom": "^6.4.2",
+    "@testing-library/user-event": "^14.5.2"
+  }
+}