docs: point the docs-site links at pages that exist

[hamidfzm]

Summary

All three deep links into the plugin docs site 404'd. Only the bare site root resolved, so anyone following "Getting Started" from this template landed on a 404 and concluded there was no docs site.

https://glyph-md.github.io/plugins/getting-started   404
https://glyph-md.github.io/plugins/recipes           404
https://glyph-md.github.io/plugins/api-reference     404

The website export writes one HTML file per markdown page, so the pages are <page>.html. The links now carry the extension.

Ordering

This targets the site layout from glyph-md/plugins#5 (export docs/ only, so its README.md becomes the site index and the pages sit at the root). Merge glyph-md/plugins#5 first, otherwise these links point at the layout that has not shipped yet and stay 404 until it does.

Not included

The types/glyph.d.ts header still says API 0.17.0 while the host is at 0.20.0. Bumping it means asserting the 0.18 to 0.20 surface is mirrored in the declarations, which needs an audit of its own.

[hamidfzm]

Not needed. The links were 404ing because the pages lived at /plugins/docs/<page>.html at the time, so there was no <page>.html at the site root. glyph-md/plugins#5 moved the pages to the root, and GitHub Pages resolves /getting-started to /getting-started.html, so the existing extensionless links work as written:

/getting-started   200
/recipes           200
/api-reference     200

Closing; nothing to change here.