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-engine/src/lib.rs

@@ -76,9 +76,9 @@ pub use sweep::{
     run_indexed, sweep, GridSpace, ListSpace, ParamRange, RandomSpace, Space, SweepError,
     SweepFamily, SweepPoint,
 };
-// `resample_block`/`MetricStats` are foundation-grade (aura-analysis, #291);
-// re-exported here (unchanged exported name set) so existing
-// `aura_engine::{resample_block, MetricStats}` consumers stay source-compatible.
+// Foundation-grade aura-analysis items, re-exported so ladder rungs without a
+// direct aura-analysis edge (e.g. aura-backtest) reach them through the engine
+// (#291; the metric-vocabulary seam rides the same path, #147).
 pub use aura_analysis::{one_sided_p_laplace, resample_block, MetricStats, MetricVocabulary};
 pub use walkforward::{
     param_stability, walk_forward, RollMode, WalkForwardError, WalkForwardResult,