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/tailwind.config.js

@@ -0,0 +1,35 @@
+/** @type {import('tailwindcss').Config} */
+export default {
+  content: [
+    "./index.html",
+    "./src/**/*.{js,ts,jsx,tsx}",
+  ],
+  darkMode: 'class',
+  theme: {
+    extend: {
+      typography: (theme) => ({
+        dark: {
+          css: {
+            '--tw-prose-body': theme('colors.gray.300'),
+            '--tw-prose-headings': theme('colors.white'),
+            '--tw-prose-links': theme('colors.blue.400'),
+            '--tw-prose-links-hover': theme('colors.blue.300'),
+            '--tw-prose-bold': theme('colors.white'),
+            '--tw-prose-counters': theme('colors.gray.400'),
+            '--tw-prose-bullets': theme('colors.gray.400'),
+            '--tw-prose-hr': theme('colors.gray.700'),
+            '--tw-prose-quotes': theme('colors.gray.200'),
+            '--tw-prose-quote-borders': theme('colors.gray.700'),
+            '--tw-prose-captions': theme('colors.gray.400'),
+            '--tw-prose-code': theme('colors.gray.200'),
+            '--tw-prose-pre-code': theme('colors.gray.200'),
+            '--tw-prose-pre-bg': theme('colors.gray.800'),
+            '--tw-prose-th-borders': theme('colors.gray.700'),
+            '--tw-prose-td-borders': theme('colors.gray.700'),
+          },
+        },
+      }),
+    },
+  },
+  plugins: [require('@tailwindcss/typography')],
+}