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.

crates/bindings/README.md

@@ -78,6 +78,9 @@ except ValueError as why:
 | `identify` | [`booksniff`](../booksniff/README.md) |
 | `series_of` | [`seriesof`](../seriesof/README.md) |
 | `parse_identifier` | [`idnorm`](../idnorm/README.md) |
+| `find_citations` | [`citefind`](../citefind/README.md) |
+| `citation_prompt` | the question `citefind --prompt` writes |
+| `merge_citation_reply` | what `citefind --merge` does with the answer |
 
 The tools that are not here are the ones a binding would gain nothing over a
 subprocess for: they read files, shell out to another program, or talk to a