Replace the dead amundsen.com spec links in source

## Summary

Three `amundsen.com` references survive in the repo. Two are dead URLs,
one of which renders into the Haddock we publish, so a reader who
follows it from Hackage gets a 404. The third is a config comment
justifying a timeout for a host that is never fetched.

## Motivation

`http://amundsen.com/media-types/collection/` redirects to
`https://amundsen.com/en-GB/media-types/collection` and returns 404.
`http://amundsen.com/media-types/collection/format/` returns 404 the
same way. The site reorganised; the media-type pages are gone.

The module header is the first thing a caller reads on Hackage, and its
only pointer to the format definition is that link.

## Scope

- `src/Data/CollectionJSON.hs:13` — the module header's "Full
documentation ... can be found at" link. User-visible in Haddock.
- `test/Data/CollectionJSONTest.hs:76` — the same URL inside a tasty
test group name. Not user-visible, but wrong for the same reason.
- `lychee.toml:9` — the comment on `timeout` cites "the amundsen.com
spec page" as a slow host worth waiting for. lychee globs
`./**/*.md`, and no Markdown file has mentioned amundsen.com since
the README moved to the GitHub spec URL, so the comment describes a
fetch that never happens. Either the justification loses that clause
or the timeout loses its reason to exist.

README.md already points at ,
which resolves. Aligning the source call sites on it keeps one spec URL
in the repo.
also resolves if a registry citation reads better in the header.

## Why CI didn't catch it

`.github/workflows/links.yml` runs lychee over `"./**/*.md"`, so
Haddock and Haskell string literals are outside what it globs. Widening
the glob to `.hs` is a plausible follow-on, but the URLs are worth
fixing regardless.

## Acceptance criteria

- [ ] Both source call sites point at a URL that resolves.
- [ ] `lychee.toml`'s timeout comment describes hosts lychee fetches.
- [ ] `cabal haddock` still builds and the header link renders.

## Additional context

Found while auditing README.md for #155; out of scope there because
that issue is README-only.

Start with the three named locations: src/Data/CollectionJSON.hs:13, test/Data/CollectionJSONTest.hs:76, and lychee.toml:9. Check the existing README.md spec link and the nearby test/config context, then run cabal haddock and the relevant test suite. Done means both source references resolve, the timeout comment matches hosts lychee fetches, and Haddock still builds with the header link rendered.

索引モデルが issue の本文から書いたものです。