docs: 🔖 mark the repository as moved before archiving

[chicio]

The last change here, and it has to land before the archive — archived repositories can't run workflows, so the notice must deploy first.

matrix-rain-webgpu now lives in chicio-blog and releases from there: 2.0.1 was published from it, with provenance naming that repo.

Every page says so, not just the landing

• Starlight's Banner is overridden rather than adding banner frontmatter to all 14 content pages. In Starlight 0.41 banner is per-page frontmatter, not a global option — I tried the global key first and the build rejected it (Unrecognized key: "banner"). An override also can't be forgotten on a page added later.
• The landing page keeps its hero — that's the library demonstrating itself, and it seemed a shame to replace it with a wall of text. Only the copy and CTAs change: the notice, then Current docs / Monorepo / npm.
• The playground gets its own strip. It's a standalone page with no Banner, and besides the landing it's the one URL people plausibly bookmarked.

Verification

built pages: 16 | carrying a moved notice: 16   (none missing)
https://chicio.github.io/chicio-blog/matrix-rain/            -> 200
https://chicio.github.io/chicio-blog/matrix-rain/playground/ -> 200

npm run check and npm run types both pass, so CI should be green.

The site stays online on purpose

Archived repositories keep serving Pages, so existing links land on the notice instead of a 404 — which is why this is a notice rather than a redirect.

After merging

1. Let the Deploy docs site workflow finish and confirm the notice is live.
2. Then archive: Settings → Archive this repository.

One thing to be aware of: the published 2.0.1 still carries homepage/repository pointing here. I'm fixing that in the monorepo so the next release links to the new home.