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

fixtures/README.md

@@ -48,6 +48,7 @@ Each record is a single file, or a folder where a format needs several files.
 | `profile-acme.json`, `profile-smithlab.json` | What those conditions ask about a team: its purpose, its funding and whom it competes with. |
 | `roster.json` | The keys that may sign, the role of each key's holder in the team, and what each key may sign. Ana is the owner, so she may revoke anyone's receipt. |
 | `layer/` | A layer of annotations on the main example (`layer.json`, `annotations.jsonl`) and the receipt that confirms them (`receipt.json`). Its claim link and its symbol name the claim `amber/k-bond` of paperclaim's example store as paperclaim references it, `claim:272XTX7C`, pinned at `claim:272XTX7C@02f47b`; the symbol names `K_r` by its key, `K_{r}`. |
+| `traces/` | A layer of traced citations on the Typst draft, which cites the main example (`layer.json`, `annotations.jsonl`, `receipt.json`): a trace a model proposed from the draft's citation of "a two-step fit" to the abstract of the main example and a person confirmed, with its receipt; a second candidate, the introduction's sentence, that a person rejected; a person's trace of the same sentence to Table 1; and a person's reply that disputes the first ([spec/18 §18.5](../spec/18-layers.md#185-traced-citations)). `vectors/traces.jsonl` resolves them after corrections. |
 | `submissions/`, `grades/` | A student's answers to exercises in the layer, and the grader's result for each. |
 | `suspect.json` | A doubtful reading raised for review: the converter's reading of an exponent in the main example, before the first correction answered it. |
 | `qa-report.json` | Reviewer error bounds for a delivery that covers two of the main example's receipts, signed by the team's owner key. |