[web-9081] The API Docs are translatable

[bgdeutsch]

What does this PR do? What is the motivation?

• wires astro's i18n to the existing shared glossary via a new @shared alias, so translations come from shared/i18n/*.json now.
• components now read their own locale from built-in Astro.currentLocale instead of requiring a lang prop threaded down from each page.
• localizes the API docs side nav, breadcrumbs, schema tables, response/code-example headings, copy buttons (all prev hardcoded to english)
• localizes the global header, footer, and mobile nav. these read from menuData.ts / footerMenus.ts, which had no locale at all and silently rendered english everywhere.
• i18n(key, lang) requires the locale, these changes introduce useTranslations(locale) which returns a bound translate(key) so call sites can't forget it. inspired by a similar pattern i saw in websites-astro.
• /{lang}/api/ now redirects to /{lang}/api/latest/ for all five locales, albeit with an open question about redirects.

Merge readiness

• Ready for merge

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AI assistance

Additional notes

to test, pull down this branch locally and start the dev server. translate.yaml config changes already landed and the shared directory is already pulled into the localization system.

Translations

• Across all locales, API docs appear translated properly.
• Left side nav is translated
• Global header/footer/mobile menu
• i18n strings ("Datadog Docs", "Overview", "Response", "Code Example", etc)
• Links such as in the nav or on the category list page point to the correct locale

Redirects
English and localized pages redirect:

• /api to /api-latest
• /api/screenboards/ to /api/latest/dashboards/
• /api/latest/downtimes/s to /api/latest/downtimes/
• etc

[github-actions]

Preview links (active after the build_preview check completes)

No changed files under hugo/content/en/, e.g. this PR only touches the Astro API docs app:

• https://docs-staging.datadoghq.com/brian.deutsch/web-9081-api-docs-translatable/api/latest/