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

sql/doc.sql

@@ -128,7 +128,7 @@ CREATE TABLE corrections (
   doc_key VARCHAR(128) NOT NULL,
   idx INTEGER NOT NULL CHECK (idx >= 1),
   id VARCHAR(32) NOT NULL,
-  op VARCHAR(16) NOT NULL CHECK (op IN ('replace', 'insert', 'delete', 'split', 'merge', 'move', 'reclassify', 'relabel', 'set')),
+  op VARCHAR(16) NOT NULL CHECK (op IN ('replace', 'insert', 'delete', 'split', 'merge', 'move', 'reclassify', 'relabel', 'set', 'emend', 'relink', 'resolve')),
   target VARCHAR(16),
   evidence TEXT NOT NULL,
   author TEXT NOT NULL,