Better landing page for downloads

A piece of feedback I've heard from many people, and for myself, is that the releases page is overwhelming and hard to navigate to find the release you want.

Also we need some way of annotating downloads on the page, e.g., you probably want install-only-stripped, you might not want the x86-64-vN binaries (uv doesn't use them), the debug binaries mean this, the static musl builds are weird, etc.

I think I'm envisioning some widget where you can filter releases by release tag, platform, Python version, and optimization level, and maybe there's some checkbox to show/hide uncommon variants.

This might roll into a larger rework of a website for python-build-standalone targeted at direct consumers of these builds (as opposed to uv users, who should have docs on uv's existing docs page).

I also very much want an API of our own over the download list, even if it points to GitHub artifact storage, so we get more control over API stability compared to having people use the raw GitHub API. I'm worried about download limits/quotas and having to drop individual .sha256sum files was a good example of this.

Start with the existing releases page and download list, then inspect how GitHub artifact storage and the raw GitHub API are currently used. Clarify whether the deliverable is the filtering and annotation widget, a stable download API, or the broader website rework; done should be defined around the selected scope and its user-facing behavior.

Written by the indexing model from the issue text.