chore(docs): remove the satteri override once starlight-github-alerts supports satteri 0.10

> 🤖 Generated by the Agentic Engineer

## Context

`docs/package.json` carries an explicit npm override:

```json
"overrides": { "satteri": "^0.10.5" }
```

It was added in #6996 to unblock the astro group bump. Without it the docs build fails rendering
`/concepts/reference-architecture`:

```
SyntaxError: The requested module 'satteri' does not provide an export named 'htmlToHast'
```

Starlight 0.42 imports `htmlToHast` from `satteri`, which exists only in satteri 0.10+. Starlight
resolves its own nested 0.10.5 at build time, but the emitted **prerender chunk** resolves `satteri`
at *runtime* from `docs/node_modules/satteri` — and that top-level copy was pinned to 0.9.5 by
`starlight-github-alerts@0.4.0`, whose declared range is `^0.9.3`.

At the time, `0.4.0` was the latest published release of `starlight-github-alerts`, so there was no
version to bump to and the override was the only available fix.

## Why this needs removing

The override forces a dependency **past its declared range**. That is safe today — the 193-page build
passes and the 29 docs files using GitHub-alert syntax all render — but it is an assumption that can
silently stop holding on any future satteri release, and it will mask a genuine incompatibility if one
appears.

## Acceptance criteria

- [ ] `starlight-github-alerts` publishes a release whose `satteri` range admits 0.10+
- [ ] that release is adopted in `docs/package.json`
- [ ] the `satteri` entry is removed from `overrides` (the `esbuild` entry is unrelated — leave it)
- [ ] `npm run build` in `docs/` completes with no `htmlToHast` error and the links validator passes

## Not actionable until upstream moves

**Blocker:** HiDeoo/starlight-github-alerts | upstream | last-verified 2026-09-12: latest published release is 0.4.0, which declares `satteri ^0.9.3`

Re-check the published version range before picking this up; if it still declares `^0.9.3`, only
update the `last-verified` result.

First check the published starlight-github-alerts version and its satteri range, as described in the blocker. Once a compatible release exists, update docs/package.json, remove only the satteri override, then run npm run build in docs/ and confirm the links validator passes without the htmlToHast error.

Written by the indexing model from the issue text.