Phase 4 — Migrate `/integrations/` to Nuxt

[n-lark]

Phase 4 — Migrate /integrations/ to Nuxt

Goal: Move the catalog and detail pages from Eleventy to Nuxt.

• Reference work first. Review ZJ's Nuxt PRs — most recent merged: nuxt: Upgrade to v4 #4953 zj-nuxt-4. The Terms page PR has reusable header/footer/layout components — reuse, don't recreate.
• Port the catalog page (src/integrations/index.njk) to a Nuxt route. Fix the ~25s page load while porting — slowness is in integrations.js (top-50 npm registry lookups + per-node GitHub /examples/ fetches).
• Port the detail page (src/_includes/layouts/integration.njk), including FlowRenderer for example flows.
• Keep static generation (Nuxt build-time fetch + SSG) for parity with today's data path. Revisit runtime/ISR only if freshness becomes a complaint.
• Remove the Eleventy integration files and add _redirects/Nuxt routes so URLs don't break.

Acceptance: /integrations/ and /integrations/{node-id}/ are served by Nuxt with feature parity, load fast, reuse the shared Nuxt header/footer. Eleventy entries deleted.