fix(seo): the pub.dev registry page lists no packages #32

What happened

/packages?registry=pub and /packages?registry=pub.dev show no packages, although 57 pub.dev packages exist. The empty page answers 200, can be indexed, and is linked from the sitemap and llms.txt. The pub.dev chip on /packages also never shows as selected.

Why

The registry filter added in #29 uses pub.dev, while the packages and the registries API use pub.

Done when

• /packages?registry=pub lists the pub.dev packages and its chip shows as selected
• The sitemap and llms.txt link to that address
• A registry page with no packages is noindex