docs(site): let a release be published by hand, and say where the versions start

[Ndevu12]

The site can version, but nothing has ever produced a second entry — gh-pages holds only latest, so the version selector has nothing to select. A version directory is created on a GitHub Release, and the site landed after v0.6.2 was cut, so the first one would not appear until v0.6.3.

Publish a version on demand

Actions → Docs → Run workflow, with a version input (e.g. 0.6.2) and an optional "point latest at it". It creates the same immutable directory a release would. The input is validated — a leading v, or anything not shaped like 1.2.3, is rejected rather than deployed under a name nothing will match.

Release-triggered publishing is unchanged, and an empty input still just refreshes latest.

Why 0.6.2 is accurate, not approximate

$ git diff --stat v0.6.2..main -- src/
(no output)

src/ is byte-identical between the v0.6.2 tag and main — everything merged since has been documentation. So these pages describe that release exactly.

Why older releases are deliberately not backfilled

I checked every tag: none carries an mkdocs.yml, so there is nothing of theirs to build. The only way to produce a 0.5.2 directory would be to republish today's pages under that number — documenting flags and behaviour 0.5.2 does not have. A plausible-looking page that is wrong is worse than no page, and it is the same defect we spent this week removing.

Instead docs/index.md now states that documented versions begin at 0.6.2, and points anyone on an older build at saw --version and -h, which describe the copy they actually have.

If you would rather have the older numbers filled in anyway, say so — it is a one-line change to the workflow input — but I would be publishing something I know to be inaccurate, so I have not done it on my own judgement.

After merge

Run the workflow once with version: 0.6.2 and "point latest at it" ticked. mike list in the job log will then show both entries, and the selector will offer them.

mkdocs build --strict clean.

Closes #1475