test: adopt the stricter ADR citation check from lite-bootstrap - #120

What

Replaces tests/test_adr_citations.py with lite-bootstrap's version, ported onto the pytestconfig.rootpath root from #119. This is the file consumers fetch from main (eof-fixer today; 23 open PRs for the rest).

Behavioural changes for every consumer:

• Bare ADR-NNNN citations are checked (existence only: docs/adr/NNNN-*.md must exist). Previously only the docs/adr/NNNN-slug.md path form was.
• .md and .toml are scanned as well as .py.
• site/ (mkdocs output) is skipped.

The invariant test is renamed test_every_adr_citation_in_the_repo_resolves. Two tests added for the new forms.

Dry run

The new file was run with pytest --rootdir=. against origin/main of every repo:

• This repo: 134 passed, 29 skipped.
• 24 of 25 consumers pass.
• that-depends fails: docs/agents/domain.md cites ADR-0007. That line is an illustrative example in agent guidance ("Contradicts ADR-0007 (event-sourced orders), but worth reopening because…"); the repo has no docs/adr/ at all. The same text is in fastapi-sqlalchemy-template and litestar-sqlalchemy-template, which are outside the mechanism (no copy of the test) but fail the same way.

So merging this turns that-depends red on its next adr-check run until that example line is reworded (for example ADR-NNNN), or the rule learns to ignore it. That is the intended pilot signal, not a reason to hold the PR, but the order of merges matters.