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/glossary.md

@@ -194,6 +194,10 @@ Text policy
 Tile
 :   One file of a transparency log served statically: 256 hashes of one level of the tree, or 256 entries, so a client fetches only the subtrees it needs. ([23.4](../spec/23-log.md#234-serving-a-log))
 
+Trace
+:   An annotation that follows one citation of a sentence to the passage of the cited paper it rests on, naming the reference it follows and, when a tool found the passage, the tool, its run, score and rank.
+Whether it still leads there is computed from both papers as current, changed, stale, unlinked or misresolved, and it is disputed while a reply assesses it. ([18.5](../spec/18-layers.md#185-traced-citations))
+
 Verdict
 :   A judgment of whether a cited passage supports a citing sentence: supports, partly, does not, or cannot tell. ([19.2](../spec/19-exercises.md#192-verdicts))