feat: comment categories; emend, relink and resolve corrections

scienting-layer/1: an optional, fixed category on comment, caveat and
question bodies (comment, context, critique, question, correction,
feedback, resource).

Corrections: emend fixes the authors' own slip and keeps what was printed
(a run's printed), never lowering fidelity or a witness match; relink sets
or removes what a citation names; resolve sets a reference's resolution.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017R7sgDNvUGWY2zFPCq2JH6

docs/glossary.md

@@ -62,6 +62,10 @@ Drift
 :   The amount that has changed below a container since an anchor on it was made, counted from the corrections: the share of the container's leaves touched by later corrections.
 It is reported as `none`, `low` or `high`, with a default threshold of a quarter. ([6.6](../spec/06-anchors.md#66-drift))
 
+Emend
+:   A correction of the authors' own typo, spelling, grammar, punctuation or wording, where the reading matches the page and the page is wrong; a `replace` fixes a misreading instead.
+The emended run keeps the text as printed, so the leaf as printed, which is what witnesses are compared with, stays what it was, and so do its match hash and its level. ([11.6](../spec/11-corrections.md#116-emendations), [3.6](../spec/03-nodes.md#36-the-plain-projection))
+
 Exercise
 :   An annotation whose body holds a prompt, an answer key and a grading rule.
 The key is anchors, a verdict, a chain, a value or planted errors, by exercise kind. ([19.1](../spec/19-exercises.md#191-exercises))