Translation freshness check: sourceHash/lastReviewed + CI warning

[spizeck]

Per docs/MULTILINGUAL.md §9 (#134, PR #149). Prevents localized content silently going stale when English sources change and enforces the human-review publication gate. Sized for a small team — no TMS.

Scope

• Convention: each content/<locale>/<page>.tsx exports sourceHash (sha1 of the English source file) and lastReviewed (YYYY-MM-DD).
• Add explicit human-review metadata for each localized page/module, using the equivalent of:
  • reviewStatus: "draft" | "approved"
  • reviewedBy
  • reviewedAt
• scripts/check-translations.mjs hashes English sources and reports stale modules.
• Dev-mode warning on stale modules.
• Switcher omits locales where a route has no approved translation — never serve English prose inside a lang="nl" page.

Human review / release contract

No localized customer-facing content may reach production unless it has explicit human approval.

AI/machine translation can produce drafts, but approval is a hard release gate.

The implementation must ensure:

• missing review metadata => not publishable
• reviewStatus !== "approved" => not publishable
• stale source hash after English changes => previous approval is no longer sufficient until the translation is reviewed again
• draft/stale translations may remain available in development/preview for review
• draft/stale translations are excluded from production locale routing, switcher visibility, sitemap alternates and hreflang
• production fails safe by omitting the locale/page rather than exposing unreviewed content

When an English source changes, the corresponding translation should become review-required again. A reviewer must update the translation, sourceHash, lastReviewed, and approval metadata before it can be published.

CI behavior

Use CI to enforce production safety.

Recommended behavior:

• informational warning for English source changes while a translation is being worked on
• blocking failure when a production-publishable locale/page would be exposed without current human approval
• English-only work must not be blocked merely because an untranslated Dutch page does not yet exist

Do not rely on a human remembering to toggle routing manually.

Acceptance

• Editing an English source page surfaces the translation as stale/review-required until reviewed and its metadata is updated.
• An unapproved translation cannot become production-visible even if the file exists.
• A stale previously approved translation cannot remain production-visible silently.
• Approved/current translations are eligible for production routing/switcher/hreflang.
• Preview/development can expose drafts for reviewer inspection without making them production-public.
• English-only PRs are not blocked solely because Dutch coverage is incomplete.