Emit trailing-slash directories so /docs/ resolves on GitHub Pages

The static export currently writes each page as page.html, which GitHub
Pages serves for /docs but not for /docs/ - the trailing-slash form that
people naturally type and paste returns a 404 today (verified live:
https://documentdb.io/docs/ is a 404 while /docs is a 200).

Setting trailingSlash: true emits docs/index.html instead, so the
trailing-slash URL serves directly and GitHub Pages 301s the bare /docs
form to /docs/. Both spellings of every route then resolve. This also
matches the Jekyll blogs section, which already uses permalink: pretty
and produces directory/index.html output.

Author: GuanzhouSong

next.config.ts

@@ -7,6 +7,9 @@ const normalizedBasePath = rawBasePath
 
 const nextConfig: NextConfig = {
   output: "export",
+  // Emit directory/index.html instead of page.html so GitHub Pages serves
+  // both /docs and /docs/ (without this, the trailing-slash form is a 404).
+  trailingSlash: true,
   ...(normalizedBasePath
     ? {
         basePath: normalizedBasePath,