feat: trace annotation body for traced citations; paperspec.traces

A trace follows one citation of a sentence of a citing paper to a passage of the
cited paper (spec/18 section 18.5). Minor change: a new body kind, optional
properties and two rules, with no valid file made invalid.

- annotation schema branch (source, selector, reference, note, verdict, proposer;
  proposer required for a Software creator); body_kind in sql/store.sql; the note
  and proposer terms of the JSON-LD context; rules layer.trace.source and
  layer.trace.target.
- paperspec.traces: resolve(annotation, citing_state, cited_state, same_as) gives
  current, changed, stale, unlinked or misresolved with open and cites; problems,
  disputes, disputed.
- fixtures/records/traces/ on writer2027fixed-ynr7.v3 and vectors/traces.jsonl
  (29 cases); check.py runs the record checks over both layers; counts, glossary,
  examples and CHANGELOG updated.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Uy4ZYbWRoCdUtWLEfigysY

docs/faq.md

@@ -107,7 +107,7 @@ A `candidate` format is complete, with vectors and fixtures, and ready to implem
 A `provisional` one is complete and expected to change as implementations gain experience.
 The provisional formats are dataset, digitization, view, project, bundle, snapshot, draft-ids, exercise, submission, grade, checklist, log-entry and checkpoint.
 
-The repository holds a reference checker (`paperspec check`), 25 vector files, five valid packages, one of them also as a zip, and 31 deliberately broken packages ([spec/00 §0.4](../spec/00-introduction.md#04-status), [spec/22](../spec/22-conformance.md)).
+The repository holds a reference checker (`paperspec check`), 26 vector files, five valid packages, one of them also as a zip, and 31 deliberately broken packages ([spec/00 §0.4](../spec/00-introduction.md#04-status), [spec/22](../spec/22-conformance.md)).
 
 ## What does it not do?