Use Sätteri 0.10 APIs - #4134

## What does this PR do?

Brings `apps/docs` up to the dependency set the documentation work
assumes. Nothing behaves
differently — `astro.config.mjs` is untouched and the rendered site is
byte-identical apart from
Starlight dropping a dead `pageHide` listener (the DOM event is
`pagehide`, so it never fired).

Verified by snapshotting `dist/` before the change and diffing after a
forced rebuild: same file
set, and that one script line is the only delta across both pages,
modulo scoped-style and asset
hashes.

Closes #1852

### The Starlight range needs a note

The ticket asked for `>=0.41.5` "a patch bump inside the existing
range". The specifier is
`>=0.41.5 <0.41.7` rather than a caret, because `^0.41.5` floats to
`0.41.7`, which does not
type-check.

`0.41.7` shipped on 5 August with `@astrojs/markdown-satteri: ^0.3.5`
and its own `satteri: ^0.9.1`
— consistent then, since `0.3.5` and `0.3.6` were still on
`satteri@^0.9.1`. On 19 August
`@astrojs/markdown-satteri@0.3.7` moved to `satteri@^0.10.3` and that
range swallowed it. Two
Sätteri copies now meet inside Starlight's own
`integrations/markdown-plugins.ts`, which
`pnpm typecheck` compiles from source, so the docs app fails to
type-check on a dependency it never
imports.

Confirmed upstream rather than a local resolution artefact: it
reproduces on `0.41.6` and `0.41.7`
with `astro` at both `7.1.1` and `7.2.4`, and forcing `satteri` to
`0.10.5` through `pnpm.overrides`
only swaps it for a different genuine error in the same file, because
Starlight's code targets
satteri 0.9.

Starlight is migrating in
[withastro/starlight#4134](withastro/starlight#4134),
blocked on an Astro release carrying
[withastro/astro#17766](withastro/astro#17766)
(merged, unreleased).
`apps/docs/README.md` records the constraint; #1865 tracks lifting it.

### Knip

The five new dependencies have no consumer yet — that is the point of
the prefactor — so each is
listed in knip's `apps/docs` ignore set with a note on which ticket
wires it up.

### Reviewer notes

- `apps/docs` gets `vitest` without `@plumix/vitest-config`, coverage,
or a `test:unit` script,
unlike every other vitest-having package. Those belong with the
content-check suite ticket.
- The cap could alternatively live in root `pnpm.overrides`, the repo's
existing mechanism for
blocking a bad upstream version. I put it on the dependency so the
acceptance criterion's floor
and the upstream break sit where a reader is already looking; happy to
move it.
- No changeset: `apps/docs` is private.

## Type of change

- [ ] Bug fix
- [ ] Feature (requires [approved
Discussion](https://github.com/withplumix/plumix/discussions/categories/ideas))
- [ ] Refactor (no behavior change)
- [ ] Documentation
- [ ] Performance improvement
- [ ] Tests
- [x] Chore (dependencies, CI, tooling)

## Checklist

- [x] `pnpm typecheck` passes
- [x] `pnpm lint` passes
- [x] `pnpm build` passes
- [ ] I have added/updated tests for my changes (if applicable)

`pnpm format`, `pnpm knip`, `pnpm test` and `pnpm install
--frozen-lockfile` also pass. No tests
added: this change installs dependencies and wires nothing up. The suite
that exercises them lands
with the content-check ticket.

## AI-generated code disclosure

- [x] This PR includes AI-generated code

## Screenshots

No admin UI change.

This PR contains the following updates:

| Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) |
|---|---|---|---|
| [@astrojs/starlight](https://starlight.astro.build) ([source](https://github.com/withastro/starlight/tree/HEAD/packages/starlight)) | [`0.41.11` → `0.42.0`](https://renovatebot.com/diffs/npm/@astrojs%2fstarlight/0.41.11/0.42.0) | ![age](https://developer.mend.io/api/mc/badges/age/npm/@astrojs%2fstarlight/0.42.0?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/@astrojs%2fstarlight/0.41.11/0.42.0?slim=true) |

---

### Release Notes

<details>
<summary>withastro/starlight (@&#8203;astrojs/starlight)</summary>

### [`v0.42.0`](https://github.com/withastro/starlight/blob/HEAD/packages/starlight/CHANGELOG.md#0420)

[Compare Source](https://github.com/withastro/starlight/compare/@astrojs/starlight@0.41.11...@astrojs/starlight@0.42.0)

##### Minor Changes

- [#&#8203;3572](withastro/starlight#3572) [`292fb17`](withastro/starlight@292fb17) Thanks [@&#8203;HiDeoo](https://github.com/HiDeoo)! - Distributes package as JavaScript files with dedicated type declaration files instead of TypeScript source files.

- [#&#8203;4121](withastro/starlight#4121) [`2623ae6`](withastro/starlight@2623ae6) Thanks [@&#8203;delucis](https://github.com/delucis)! - Simplifies markup for Starlight’s mobile menu toggle

  **⚠️ Potentially breaking change:** If you use a theme plugin, custom styles, or component overrides targeting the `MobileMenuToggle` button or `PageFrame` components, you may need to adjust these for the new markup. The button is no longer wrapped in a `<starlight-menu-button>` custom element and no longer uses the `aria-expanded` attribute. Instead, you can use the `.sl-menu-button` class name to target the button and the `:popover-open` pseudo-class to style the menu open state specifically.

  In the following example, custom styles for the menu button are updated for the new approach:

  ```diff
  - starlight-menu-button button {
  + .sl-menu-button {
    color: var(--sl-color-text);
  }

  - starlight-menu-button[aria-expanded='true'] button {
  + .sl-menu-button:has(~ :popover-open) {
    color: var(--sl-color-text-accent-high);
  }
  ```

  See [`MobileMenuToggle.astro`](https://github.com/withastro/starlight/blob/main/packages/starlight/components/MobileMenuToggle.astro) and [`PageFrame.astro`](https://github.com/withastro/starlight/blob/main/packages/starlight/components/PageFrame.astro) on GitHub for the full source code of the updated components.

- [#&#8203;3572](withastro/starlight#3572) [`292fb17`](withastro/starlight@292fb17) Thanks [@&#8203;HiDeoo](https://github.com/HiDeoo)! - Removes the `tagline` configuration option, which was never used.

  If your configuration included a `tagline` option, you can safely remove it without any replacement.

- [#&#8203;4134](withastro/starlight#4134) [`6135f01`](withastro/starlight@6135f01) Thanks [@&#8203;HiDeoo](https://github.com/HiDeoo)! - Updates internal `@astrojs/mdx`, `@astrojs/markdown-satteri`, and `satteri` dependencies.

  ⚠️ **BREAKING CHANGE:** The following minimum versions are now required:

  - `astro` v7.2.10 or later
  - `@astrojs/markdown-satteri` 0.4.0 or later (if you use it)
  - `@astrojs/markdown-remark` 7.3.0 or later (if you use it)

  Please update Starlight and Astro together:

  ```sh
  npx @astrojs/upgrade
  ```

- [#&#8203;4121](withastro/starlight#4121) [`2623ae6`](withastro/starlight@2623ae6) Thanks [@&#8203;delucis](https://github.com/delucis)! - Refactors Starlight’s mobile menu toggle to work when JavaScript fails or is disabled

  ⚠️ **BREAKING CHANGE:** This release drops official support for Chromium-based browsers prior to version 116 (released August 2023), Safari-based browsers prior to version 17.0 (released September 2023), and Firefox prior to version 125 (released April 2024). You can find a list of currently supported browsers and their versions using this [browserslist query](https://browsersl.ist/#q=%3E+0.5%25%2C+not+dead%2C+Chrome+%3E%3D+116%2C+Edge+%3E%3D+116%2C+Firefox+%3E%3D+125%2C+Safari+%3E%3D+17.0%2C+iOS+%3E%3D+17.0%2C+not+op_mini+all).

  This change also removes the `data-mobile-menu-expanded` attribute, which was previously added to `<body>` while the mobile menu is open. If you have custom code that was depending on this attribute, you will need to update it to use a new selector to check if the mobile menu is open.

  In the following example, a custom background colour for the site header while the menu is open is updated for the new approach:

  ```diff
  - [data-mobile-menu-expanded] header {
  + body:has(sl-sidebar-pane:popover-open) header {
    background-color: var(--sl-color-bg);
  }
  ```

</details>

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