Complete conversion to Nuxt

The site is served by two generators: Eleventy renders most pages from `src/`, Nuxt renders the rest, and `nuxt/server/middleware/legacy.ts` proxies between them in dev. This is the last stretch of that migration: every remaining page moves to Nuxt, then Eleventy comes out.

## Order

1-17 are independent and target `main`, but they all touch the same two registry files (`legacy.ts`, `nuxt.config.ts`), so expect a small rebase after each merge. Merge top to bottom.

1. https://github.com/FlowFuse/website/pull/5778
2. https://github.com/FlowFuse/website/pull/5779
3. https://github.com/FlowFuse/website/pull/5780
4. https://github.com/FlowFuse/website/pull/5781
5. https://github.com/FlowFuse/website/pull/5782
6. https://github.com/FlowFuse/website/pull/5783
7. https://github.com/FlowFuse/website/pull/5784
8. https://github.com/FlowFuse/website/pull/5785
9. https://github.com/FlowFuse/website/pull/5786
10. https://github.com/FlowFuse/website/pull/5787
11. https://github.com/FlowFuse/website/pull/5788
12. https://github.com/FlowFuse/website/pull/5789
13. https://github.com/FlowFuse/website/pull/5790
14. https://github.com/FlowFuse/website/pull/5791
15. https://github.com/FlowFuse/website/pull/5792
16. https://github.com/FlowFuse/website/pull/5793
17. https://github.com/FlowFuse/website/pull/5794
18. https://github.com/FlowFuse/website/pull/5795
19. https://github.com/FlowFuse/website/pull/5796

18 and 19 are drafts because 18 deletes `src/` and the dev proxy, which against today's `main` would delete pages 2-17 are still migrating. They are based on `nuxt/eleventy-teardown-base`, a scaffolding branch holding the combined state of 1-17, so their diffs show only their own change. Retarget both to `main` once 1-17 have landed, then delete that branch.

## Notes

- https://github.com/FlowFuse/website/pull/5694 overlaps 17: it adds its own `nuxt/lib/blueprints-sync.mjs` and rewrites the same workflow. Land it first and rebase 17 onto it.
- Every route was checked against the published page before this was raised.
- https://github.com/FlowFuse/blueprint-library/pull/182 goes with 17: a blueprint whose markdown heading is a link nests an `` inside the anchor `@nuxt/content` wraps headings in, which HTML cannot represent, so the blueprint page logs a hydration mismatch. 11ty tolerated it. It was the only linked heading of the 19 blueprints, and the link was dead anyway.

Start with nuxt/server/middleware/legacy.ts and nuxt.config.ts, then review pull requests 5778-5796 in the stated order. The migration is complete when every remaining page is served by Nuxt and Eleventy, src/, and the development proxy can be removed; drafts 5795 and 5796 cover that teardown after the earlier work lands.

Written by the indexing model from the issue text.