Detect stale docs.livestore.dev deploys via version meta tag

[schickling-assistant]

Problem

`https://docs.livestore.dev\` can fall behind the latest LiveStore release if the Netlify deploy fails or never runs. Nothing currently surfaces a stale docs deploy until a user complains.

Solution

1. Docs build emits `<meta name="livestore-version" content="…">` from `docs/astro.config.ts` (Starlight `head` option). This is a stable, machine-readable marker reserved for the health check so renaming the site title can't accidentally break the probe.
2. Daily workflow (09:15 Europe/Berlin) + GitHub Release `published` hook + manual dispatch fetches the docs landing page, parses the meta tag, and compares it against npm `latest`.

Behaviour:

• match: `::notice::docs version matches npm latest`.
• release-triggered mismatch within 30m of `published_at`: notice only (lets the docs deploy catch up).
• otherwise: opens (or warms) a `bug docs` issue titled `docs.livestore.dev version drifted from npm latest`.

Deferred sub-features

• Auto-trigger docs redeploy on mismatch: the spec mentioned dispatching `deploy-prod.yml` with `target=docs`; this workflow does not exist in the repo today (docs go through Netlify), so the check escalates by opening an issue instead of silently re-triggering deploys.
• Discord `#release-alerts` notification: no Discord webhook secret is configured in the repo (`gh secret list` confirmed), so the check relies on the GitHub issue alone. If a webhook is added later, hook it in alongside `openIssue()` in `scripts/src/commands/health/docs-version.ts`.

Observation about existing version markers

Today the docs site only exposes the version through `og:site_name` (`LiveStore (0.4.0)`), which doubles as the human-readable site title. Tying a health check to a render-cosmetic string is fragile — hence the dedicated `livestore-version` meta tag.

Validation

• `bun scripts/src/commands/health/docs-version.ts --trigger=workflow_dispatch --dry-run` runs locally; it correctly detects that production currently lacks the meta tag (it will once this PR ships).
• `devenv tasks run lint:check` passes.
• `devenv tasks run genie:run --mode before --no-tui` regenerates the workflow cleanly.

Files

• `docs/astro.config.ts` — adds the `head` option emitting the meta tag.
• `.github/workflows/health-docs-version.yml.genie.ts` — workflow source.
• `scripts/src/commands/health/docs-version.ts` — fetch + compare + issue management.
• `CHANGELOG.md` — entry under `### Internal Changes > Development Tooling`.

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