feat(registry): add next-intl localized routes

[bntvllnt]

Summary

• Add next-intl routing for English and French registry app pages, with localized metadata, hreflang alternates, sitemap entries, and locale-aware navigation/chrome.
• Move MDX page content to content/pages/<slug>/<locale>.mdx, add French pages, and add a CI translation check for required default-locale MDX.
• Keep machine endpoints canonical while adding localized llms routes and /r/<name>.<locale>.json description overlays.
• Remediate the current-head i18n/SEO blocker for comparison routes: /fr/vs and /fr/vs/shadcn now have French metadata and visible French body/table copy, so the advertised French canonical, sitemap, and hreflang alternates no longer point at English-only comparison pages.

Dependency tradeoff

• Adds next-intl to the registry app only. This brings next-intl, use-intl, and @formatjs/* runtime packages, but avoids a bespoke i18n router/message loader and matches the issue request.

Current head

• d66a08c69581cfc3ff69cd0213461890be0c4bc9

Validation

Latest remediation validation on d66a08c69581cfc3ff69cd0213461890be0c4bc9:

• PASS: pnpm -F @vllnt/ui-registry exec tsc --noEmit --project tsconfig.json
• PASS: targeted ESLint for edited comparison route files: pnpm -F @vllnt/ui-registry exec eslint 'app/[locale]/vs/page.tsx' 'app/[locale]/vs/shadcn/page.tsx'
• PASS: git diff --check
• FAIL baseline/unrelated: pnpm -F @vllnt/ui-registry lint still exits 1 with 221 existing errors outside the edited comparison files, including app/manifest.ts, app/mcp/route.ts, app/robots.ts, lib/jsonld.ts, registry scripts, and types/registry.ts.
• RUNNING after push: pnpm build and pnpm test:once are being re-run for d66a08c69581cfc3ff69cd0213461890be0c4bc9; this section will be updated if either result differs from the prior local pass.

Prior branch validation retained from earlier HEAD:

• pnpm install --frozen-lockfile
• pnpm -F @vllnt/ui lint
• pnpm -F @vllnt/ui exec tsc --noEmit --project tsconfig.build.json
• pnpm -F @vllnt/ui-registry exec tsc --noEmit --project tsconfig.json
• pnpm build
• pnpm test:once
• pnpm -F @vllnt/ui-registry check:translations
• pnpm -F @vllnt/ui check:use-client
• pnpm -F @vllnt/ui exec tsx scripts/check-story-coverage.ts
• pnpm -F @vllnt/ui exec tsx scripts/verify-stories.ts
• pnpm -F @vllnt/ui build-storybook
• git diff --check
• Targeted registry ESLint over touched runtime route/component/lib files, including localized routes and llms routes.

Runtime smoke

After pnpm build, ran pnpm -F @vllnt/ui-registry exec next start -p 3011 and verified:

• curl -I http://localhost:3011/en/llms.txt -> 308 to http://localhost:3011/llms.txt
• curl -I http://localhost:3011/en/llms-full.txt -> 308 to http://localhost:3011/llms-full.txt
• curl -I http://localhost:3011/request-component -> 200 with rewrite to /en/request-component and NEXT_LOCALE=en
• curl http://localhost:3011/r/button.fr.json -> localized overlay JSON with locale: "fr", sourceLocale: "en", and canonical /r/button.json
• curl http://localhost:3011/fr/llms.txt | head -8 -> French llms header/content

CI status

• Re-running for current head d66a08c69581cfc3ff69cd0213461890be0c4bc9 after the comparison-route remediation push.

Closes #281

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Project	Deployment	Actions	Updated (UTC)
storybook	Ready	Preview, Comment	May 14, 2026 2:05pm
ui.vllnt.ai	Canceled		May 14, 2026 2:05pm