citefind: the references in a bibliography, and what could not be read off them

Cuts a reference list into entries — at the note numbers where there are any,
at the layout where there are not — and reads each as far as its punctuation
allows. Fields that would not parse are named in `unsettled` rather than
guessed at, and `--prompt` asks a model about exactly those and no others.

Over 202 real reference sections from the corpus: 8,566 references, 95% with
a title, 82% with a year, 46% settling every field with no model involved.
A title is refused where the entry was never divided, so no record reports
its own text back as the work it cites.

`ibid.` is flagged and left alone — it points at a work, and the entry does
not say which. A rule of dashes is filled in, because the style defines it as
the author above.

chunkmd gains `note_starts` and `cites_something`: recognising a page of
notes and splitting one are the same knowledge, and two copies of that
pattern would drift.

README.md

@@ -34,6 +34,7 @@ Each tool installs by name, so you can take one without taking the rest.
 | [`seriesof`](crates/seriesof/README.md) | The series a book belongs to, and which volume this is |
 | [`idnorm`](crates/idnorm/README.md) | DOIs, ISSNs, ISBNs and arXiv ids, read and checked |
 | [`bibfetch`](crates/bibfetch/README.md) | What a register says about an identifier |
+| [`citefind`](crates/citefind/README.md) | The references in a bibliography or a page of notes |
 | [`mdscrub`](crates/mdscrub/README.md) | Converted markdown in, clean markdown out |
 | [`mdsplit`](crates/mdsplit/README.md) | One markdown file into the works inside it |
 | [`chunkmd`](crates/chunkmd/README.md) | Markdown into passages that carry their page, chapter and role |