docs: what citefind reads, and a citation graph built out of the books

The README now lists the forms it handles with an example of each, says that
where the italics sit is what decides whether they are the title or the
journal, and sets out what it refuses and why — scripture, Migne, a
contributor's biography, a note that only thanks people, a page footer.

Recipes gains "What a book leans on": one bibliography read, then the same
over a shelf, counted per citing book so a work cited forty times in one
bibliography still counts once. Every command was run — thirty converted
books gave 14,481 references, 10,536 naming a work, in about a second.

`records.md` now points at the five tools whose record shapes live in their
own pages rather than in `corpus-core`.

And pandoc escapes an underscore, so the rule of them that stands in for a
repeated author arrives as `\_\_\_\_\_` and was not being recognised.

docs/recipes.md

@@ -214,6 +214,109 @@ $ pandoc -t commonmark chapter.xhtml | mdscrub | chunkmd --min-tokens 10
 Every chunk carries the page it came from and the chapter it sits under, which
 is what lets a search result cite itself.
 
+## What a book leans on
+
+The bibliography is the one part of a book that is already structured. Every
+entry names a work, and most name it in one of a handful of shapes that have
+not changed in a century — so `citefind` reads it without asking anybody
+anything.
+
+```
+$ citefind bibliography.md | head -1
+{"v":1,"idx":0,"text":"Abogunrin, S. O. “The Three Variant Accounts of Peter’s Call: A Critical and Theological Examination of the Texts.” *New Testament Studies* 31 (1985): 587–602.","marker":null,"authors":["Abogunrin, S. O."],"year":1985,"title":"The Three Variant Accounts of Peter’s Call: A Critical and Theological Examination of the Texts","container":"New Testament Studies","pages":"587–602","ids":[],"kind":"article","continuation":false,"unsettled":[]}
+```
+
+Whose work a book rests on, counted:
+
+```sh
+citefind bibliography.md \
+  | jq -r 'select(.authors | length > 0) | .authors[0]' \
+  | sort | uniq -c | sort -rn | head
+```
+
+```
+  64 Yates
+  26 Quigley
+  23 Bulgakov, Sergius
+  17 Lorenz, K.
+```
+
+What it reads, and what it reaches for:
+
+```sh
+citefind bibliography.md | jq -r .kind | sort | uniq -c | sort -rn
+```
+
+```
+4200 other
+3356 book
+ 808 chapter
+ 700 article
+ 300 web
+```
+
+The identifiers it finds, checked and resolved against a register:
+
+```sh
+citefind bibliography.md \
+  | jq -r '.ids[]? | select(.kind == "doi") | .id' \
+  | idnorm | bibfetch
+```
+
+### Across a whole shelf
+
+Every book's bibliography, cut out of the converted markdown and read:
+
+```sh
+for f in converted/*.md; do
+  awk '/^#+ *(Bibliography|References|Works Cited|Notes)/{on=1} on' "$f" \
+    | citefind 2>/dev/null \
+    | jq -c --arg from "$(basename "$f" .md)" '. + {citing: $from}'
+done > citations.ndjson
+```
+
+Over thirty converted books that was 14,481 references, 10,536 of them naming
+a work, in about a second. A book whose heading matched but whose section was
+empty exits `1` and says so on stderr, which is why the loop sends it
+nowhere.
+
+Which works the shelf agrees on — cited by the most different books:
+
+```sh
+jq -r 'select(.title) | [.citing, (.title | ascii_downcase)] | @tsv' citations.ndjson \
+  | sort -u | cut -f2 | uniq -c | sort -rn | head
+```
+
+Counted per citing book rather than per entry, so a work cited forty times in
+one bibliography still counts once. On a shelf whose books share a subject
+this is the spine of the field; on one that does not, it is mostly ones.
+
+That is a citation graph, built out of the books themselves, with nothing
+running but a parser.
+
+### What it could not read
+
+Every record names the fields it could not settle. A bibliography set in a
+style the parser does not know, or a chunk that began part-way through an
+entry, shows up here rather than as a confident wrong answer:
+
+```sh
+citefind bibliography.md | jq -r 'select(.unsettled | length > 0) | .text'
+```
+
+`--prompt` writes a question about exactly those entries and no others, for a
+model of your choosing. Nothing is sent from here:
+
+```sh
+citefind --prompt bibliography.md | ollama run qwen3:8b > reply.json
+citefind --merge reply.json bibliography.md
+```
+
+A reply fills in only the fields that were asked about; a model that
+volunteers a better title for an entry whose title was read off the page is
+overruled. Most bibliographies have nothing to ask about, and `--prompt`
+exits `1` and writes nothing when that is so.
+
 ## A collected edition into one record per work
 
 Forty books in one file, indexed whole, means a query for any of them returns a