fix: add transpilePackages for ESM-only markdown deps (#147)

Add react-markdown and remark-gfm to transpilePackages in next.config.js
so Next.js transpiles these ESM-only modules correctly in all environments.
This fixes 'Module not found: Can't resolve remark-gfm' build errors.

Fixes #142

next.config.js

@@ -2,6 +2,8 @@
 const nextConfig = {
   output: 'standalone',
   turbopack: {},
+  // Transpile ESM-only packages so they resolve correctly in all environments
+  transpilePackages: ['react-markdown', 'remark-gfm'],
   
   // Security headers
   async headers() {