Run spellchecker on PRs

[MattiasBuelens]

This uses spellchecker-cli to spellcheck all Markdown and MDX files that are changed by a pull request.

This is obviously going to raise a lot of false negatives at first while we build up our custom dictionary. We'll see how this goes. 😅

[github-actions]

PR Preview Action v1.8.1
🚀 View preview at https://THEOplayer.github.io/documentation/pr-preview/pr-532/
Built to branch gh-pages at 2026-02-25 08:59 UTC. Preview will be ready when the GitHub Pages deployment is complete.

[MattiasBuelens]

Some issues I've found so far:

• It doesn't seem to recognize JSX inside MDX? I'm seeing spelling errors for JavaScript variables and JSX components. 😕
• It doesn't recognize custom header IDs, such as:

  ### Hello World {#my-explicit-id}

  This is probably due to it being a Docusaurus-only Markdown feature... We might need a custom plugin to detect and ignore these, similar to retext-syntax-urls.