Archive, part 2a-i: an archived repository leaves the web home's apps, the explorer's default view and the web inbox, assigned work included #2493

Part of #2454, split after pull #2463's reviews: the web half.

Done looks like:

• [ ] listReposVisibleTo / listReposWritableTo take withoutArchived (off by default). The home's apps, the asks candidates and decisions, needs-you, askedRepos and the stalled-steps reader leave archived repositories out.
• [ ] askCandidatesFor's assigned loop skips a repository that is archived, so work assigned to the viewer there does not count in the inbox.
• [ ] The explorer hides archived repositories unless the line says archived:yes; its toggle reads "Show archived" and exposes its state (aria-current or aria-pressed).
• [ ] The docs say which lists still show an archived repository (/apps, search, the palette, the repository API).
• [ ] An archived repository's page still answers 200.
• [ ] Tests: absent from home, explorer and inbox (including an issue assigned to the viewer), present with archived:yes, its page answers 200. Run the asks, explore and home tests and quote the result.