#3999 Support search and filters as URL query parameters on /extensions

The extension registry search only works through the search box on the page. Opening https://swamp-club.com/extensions?q=vados returns the default listing (the newest 24 of about 1,900 extensions), not the matches for “vados”.

This matters for anything that reads the registry by URL rather than in a browser, such as AI assistants with a web-fetch tool, scripts or link checkers. They can’t type into the search box, so a query URL is their only way in. In practice, an assistant asked about an existing extension (@gklijs/vados) concluded it didn’t exist, because the URL it tried showed an unfiltered list. It also means people can’t share a link to a set of search results.

Request:

Have /extensions read the search from the URL (?q=, or whatever name you choose), and render the results on the server so they appear in the page HTML without JavaScript. Reflect the existing filters in the URL too, with the same names as the CLI flags: content-type, label, platform, collective, sort and channel. Update the URL when someone searches in the box, so the results page can be bookmarked and shared.