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

registry/rules.json

@@ -448,6 +448,16 @@
       "description": "The exercise kind is unknown.",
       "chapter": "spec/22-conformance.md"
     },
+    {
+      "id": "layer.trace.source",
+      "description": "A trace's passage is not in the document its source names, its source is the citing document, its selector has no AnchorSelector, or its TextQuoteSelector does not repeat the anchor's plain quote.",
+      "chapter": "spec/18-layers.md"
+    },
+    {
+      "id": "layer.trace.target",
+      "description": "A trace's target is not a leaf with runs of the citing document selected by an AnchorSelector, or its sentence does not cite the reference the trace names.",
+      "chapter": "spec/18-layers.md"
+    },
     {
       "id": "package.file.canonical",
       "description": "A JSON or JSON Lines record is not in canonical JSON.",