Fetch Djot grammar dynamically instead of committing it (#96)

* Fetch Djot grammar dynamically instead of committing it

- Add postinstall script to fetch grammar from djot-intellij
- Add grammars directory to .gitignore
- Remove stale local copy (workflow already fetches at build time)

This ensures local development always uses the latest grammar
from upstream, staying in sync with CI builds.

* Add documentation site section to CONTRIBUTING.md

Author: dereuromark

.gitignore

@@ -21,3 +21,4 @@
 /docs/node_modules/
 /docs/.vitepress/cache/
 /docs/.vitepress/dist/
+/docs/.vitepress/grammars/

CONTRIBUTING.md

@@ -114,6 +114,30 @@ public function testFeatureContains(): void
 }
 ```
 
+## Documentation Site
+
+The documentation is built with [VitePress](https://vitepress.dev/).
+
+### Local Development
+
+```bash
+cd docs
+npm install    # Fetches Djot grammar from djot-intellij automatically
+npm run docs:dev
+```
+
+This starts a dev server at `http://localhost:5173/djot-php/` with hot reload.
+
+The Djot syntax highlighting grammar is fetched from [djot-intellij](https://github.com/php-collective/djot-intellij) during `npm install` (via postinstall hook), ensuring you always have the latest version.
+
+### Building
+
+```bash
+cd docs
+npm run docs:build
+npm run docs:preview  # Preview the build
+```
+
 ## Pull Request Guidelines
 
 1. Create a feature branch from `master`