audit: cycle metric-vocabulary tidy — ledger records the retired #147 deferral

Cycle-close audit (architect: drift_found, design core clean). What holds,
architect-confirmed: C18 bit-identity for RunMetrics (prose derived
byte-identically, rng order preserved, registry suite unchanged); the C10
wall (monomorphic R-gates, r_based in the R vocabulary, cross-vocabulary
refusal tested both ways — no leak); C28 direction (trait in aura-analysis,
vocabulary supplied from the outer rungs, zero Cargo edge changes); C1
determinism pinned through the generic path.

Drift items, all resolved as fixes in this commit:
- design ledger: the C28 #147 disposition now records item 2 SHIPPED (the
  A1 cut) with A2 still deliberately deferred; the #136 one-implementor
  clause carries a supersession note (the IC is the second implementor).
- seven stale doc comments describing the pre-#147 or mid-cycle state
  (analysis trait + estimator docs, registry check_r_metric C9 claim,
  engine re-export note, campaign PER_MEMBER_METRICS roster note,
  member-seam guard comment, research vocabulary note) updated to the
  shipped state.
- R_BASED_METRICS is now oracle-pinned against RunMetricKey::r_based()
  in the vocabulary test (it feeds the NonRMetric refusal prose; a
  divergence would have misreported the R-gate silently).

Noted, not amended (history stays): commit 6744f67's body says 'three
syntax-only edits' where the test module actually took five.

No regression scripts are configured (the bench is report-only); the
architect review is the gate. Verification: extended vocabulary test,
campaign suites, analysis/research suites green; clippy --workspace
-D warnings clean.

refs #147

crates/aura-registry/src/lib.rs

@@ -793,8 +793,9 @@ pub struct Generalization {
 }
 
 /// Validate that `metric` is a known, R-based ranking key — the data-free pre-check
-/// the CLI runs before evaluating any instrument. The registry owns metric truth
-/// (C9), so the CLI never duplicates the R-set.
+/// the CLI runs before evaluating any instrument. The R classification lives in the
+/// backtest vocabulary (`RunMetricKey::r_based`, C10); this gate is the registry's
+/// monomorphic wall around it, so the CLI never duplicates the R-set.
 pub fn check_r_metric(metric: &str) -> Result<(), RegistryError> {
     let key = <RunMetrics as MetricVocabulary>::resolve(metric).ok_or_else(|| {
         RegistryError::UnknownMetric {