feat(markdown-editor): implement wysiswyg markdown editor with live preview

- Build Go backend with Cobra CLI and REST API
  - CRUD operations for markdown files (GET, POST, PUT, DELETE)
  - File storage with flat .md file structure
  - Comprehensive logrus logging with JSON format
  - Static asset serving for frontend

- Build React/TypeScript frontend with Tailwind CSS
  - Markdown editor with live GFM preview
  - File management UI (list, create, open, delete)
  - Theme system (Dark/Light/System) with persistence
  - Responsive design (320px mobile, 1920px desktop)

- Add comprehensive test coverage
  - Backend: API, storage, and logger tests (13 tests passing)
  - Frontend: Editor and App component tests

- Setup Nix development environment with Go, Node.js, and TypeScript

frontend/package.json

@@ -0,0 +1,44 @@
+{
+  "name": "markdown-editor-frontend",
+  "version": "0.1.0",
+  "private": true,
+  "dependencies": {
+    "@testing-library/jest-dom": "^6.6.3",
+    "@testing-library/react": "^16.1.0",
+    "@testing-library/user-event": "^14.5.2",
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1",
+    "react-markdown": "^9.0.1",
+    "react-scripts": "5.0.1",
+    "react-syntax-highlighter": "^15.5.0",
+    "react-textarea-autosize": "^8.5.7",
+    "web-vitals": "^2.1.4"
+  },
+  "devDependencies": {
+    "@types/jest": "^29.5.14",
+    "@types/node": "^22.8.6",
+    "@types/react": "^18.3.12",
+    "@types/react-dom": "^18.3.1",
+    "@types/react-syntax-highlighter": "^15.5.13",
+    "@types/react-textarea-autosize": "^8.5.6",
+    "autoprefixer": "^10.4.20",
+    "eslint": "^9.14.0",
+    "eslint-config-react-app": "^7.0.1",
+    "postcss": "^8.4.47",
+    "tailwindcss": "^3.4.14",
+    "typescript": "^5.6.3"
+  },
+  "scripts": {
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test",
+    "eject": "react-scripts eject"
+  },
+  "eslintConfig": {
+    "extends": ["react-app", "react-app/jest"]
+  },
+  "browserslist": {
+    "production": [">0.2%", "not dead", "not op_mini all"],
+    "development": ["last 1 chrome version", "last 1 firefox version", "last 1 safari version"]
+  }
+}