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

tools/README.md

@@ -75,8 +75,8 @@ A node's five values depend only on its own subtree, so after a correction the o
 `paperspec check` compares the result after every correction with a slow computation that projects each node from its whole subtree.
 
 Other repositories of the project do not reimplement the specification: they install this repository as the Python package `paperspec`, from the Gitea package registry or as a git pin ([deploy/](../deploy/README.md#install-from-the-registry)), and import the oracle from it, so that every key, identifier, canonical JSON string, package check and database form comes from one piece of code.
-The library surface they use is `keys`, `text`, `jcs`, `package`, `db`, `schema` and `rights`, with the schemas, SQL and vectors as package data: `paperspec.resources.path("sql")` finds a folder in an installed wheel and in an editable install alike.
-The vectors travel with the package, but `resolve.jsonl`, `grading.jsonl` and `targets.jsonl` name a fixture package, and the fixtures stay in the repository.
+The library surface they use is `keys`, `text`, `jcs`, `package`, `db`, `schema`, `rights` and `traces`, with the schemas, SQL and vectors as package data: `paperspec.resources.path("sql")` finds a folder in an installed wheel and in an editable install alike.
+The vectors travel with the package, but `resolve.jsonl`, `grading.jsonl`, `targets.jsonl` and `traces.jsonl` name a fixture package, and the fixtures stay in the repository.
 The package needs Python 3.14, the only version with the Unicode 16.0 character data the specification pins, and refuses to import on any other.
 Importing any of its modules needs only the standard library.
 Schema validation (`schema`, and with it `package.validate` and `corrections.gate`) needs `paperspec[schema]` (`jsonschema` and `referencing`), and HKDF and Ed25519 in `crypto`, which the signature and receipt checks use, need `paperspec[crypto]`.