dx: check-links retries 20 s timeouts in full, and the local loop needs a documented Node version #86

Why it matters
Small developer-experience items that do not justify separate issues:

• check-links.mjs retries every "dead" result including 20-second timeouts (:76), so one dead host costs a worker 40 s; fine at 414 entries with 8 workers, slow at 2,000. A shorter retry timeout (5 s) or no retry on TimeoutError keeps the weekly run bounded.
• .nvmrc says 24, package.json engines says >=22, the README says "Node 22 or newer", and CI runs 24. Pick one statement (for example "22 or newer; CI uses 24") and say it in one place.
• new-entry prints next steps but hands over the template with inline comments that the parser mishandles (see the validator typing issue); once that is fixed, have it print the validate command for the single new file.
• 95 of the 120 format values belong to no filter group in site/format-vocabulary.json, so the Format filter cannot reach them; either group them or document that only grouped formats are filterable.

Evidence

• site/check-links.mjs:33-34, 76; .nvmrc; package.json engines; README.md "Run the checks" details block; site/format-vocabulary.json.

Suggested approach
Handle each bullet in one small PR.

Done when
The retry is bounded, the Node statement is consistent, and the format filter either reaches every format or the docs say which it reaches.