Seven broken intra-doc anchors in docs/api/collections.md (entity-encoded generic headings slug differently than assumed)

[marius-bughiu]

What

Seven intra-document links in docs/api/collections.md point at anchors that do not exist, so clicking them scrolls nowhere.

Used	Occurrences	Real anchor
#celerityset-t-thasher	6	#celeritysett-thasher
#swissset-t-thasher	1	#swisssett-thasher

Why

The headings are entity-encoded generics — ## CeleritySet<T, THasher>. GitHub's slugger lowercases the rendered text and deletes <, > and , without substituting a separator, so CeleritySet<T, THasher> becomes celeritysett-thasher (double t, from …Set + T), not the intuitive celerityset-t-thasher.

Verified against the live rendering rather than inferred:

gh api repos/marius-bughiu/Celerity/contents/docs/api/collections.md \
  -H "Accept: application/vnd.github.html" | grep -oE 'id="user-content-[a-z0-9-]*"'

returns user-content-celeritysett-thasher and user-content-swisssett-thasher. The same command confirms ### IReadOnlyDictionary<TKey, TValue?> renders as ireadonlydictionarytkey-tvalue — so the pattern is consistent, and the six-plus-one links are simply wrong.

Fix

Correct the seven links. Worth pairing with a CI guard, since this class of rot is invisible in review: a step that renders each markdown file through the GitHub HTML endpoint (or a local slugger with the same rule), collects every id="user-content-…", and fails when a ](#fragment) in the same file has no matching id. That is a handful of lines and would also catch the next heading rename.

Scope is the whole docs/ tree plus README.md, not just collections.md — the check above was only run on the one file.

Found while adding the IDictionary<,> section in #338; deliberately left out of that PR to keep it to one concern.