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)

frontend/tailwind.config.js

@@ -0,0 +1,33 @@
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  content: [
+    "./index.html",
+    "./src/**/*.{js,ts,jsx,tsx}",
+  ],
+  theme: {
+    extend: {
+      colors: {
+        dark: {
+          bg: '#1a1a2e',
+          surface: '#16213e',
+          text: '#eaeaea',
+          textMuted: '#a0a0a0',
+        },
+        light: {
+          bg: '#ffffff',
+          surface: '#f8f9fa',
+          text: '#333333',
+          textMuted: '#666666',
+        },
+        system: {
+          bg: 'var(--system-bg)',
+          surface: 'var(--system-surface)',
+          text: 'var(--system-text)',
+          textMuted: 'var(--system-text-muted)',
+        },
+      },
+    },
+  },
+  plugins: [],
+  darkMode: 'class',
+}