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/overview.md

@@ -56,7 +56,7 @@ It appears inside hashed data and test vectors, and it is separate from the repo
 | [registry/](../registry/README.md) | The list of formats, the rule IDs a checker reports, download-stamp rules, and default rights requirements. |
 | [tools/](../tools/README.md) | How to run the reference commands: `paperspec check` checks everything, `paperspec build` rebuilds the fixtures and vectors, and `paperspec load` loads packages into SQLite. |
 | [src/paperspec/](../src/paperspec/) | The oracle, a compact implementation of every rule, which the other repositories of the project install as the Python package `paperspec`. |
-| [vectors/](../vectors/README.md) | 25 files of test vectors: inputs and the exact outputs every implementation must compute. |
+| [vectors/](../vectors/README.md) | 26 files of test vectors: inputs and the exact outputs every implementation must compute. |
 | [fixtures/](../fixtures/README.md) | Five valid example packages, one of them also as a zip, 31 deliberately broken ones that each break one named rule, example records, and the test keys that signed them. All text is synthetic. |
 | [sql/](../sql/README.md) | Tables for SQLite, Dolt and PostgreSQL, and a SQLite bundle with full-text search. |
 | [context/](../context/README.md) | The JSON-LD context that makes annotation layers W3C Web Annotations. |