feat(ruview-gamma): RuVector self-learning layer (ADR-250 §10 items 3-6)

New ruvector module: anonymized ProfileStore (one-way SHA-256 hashed tags,
safe-session scores only), deterministic exact kNN, cohort warm-start (a new
person's optimizer seeded from the k nearest responders as down-weighted GP
pseudo-observations), physiological drift detection (Welford centroid with
stimulus-input fields masked out of the distance), and deterministic k-means
response clustering.

Honesty guarantees, asserted in tests: cohort priors carry >=25x the
real-observation noise, are excluded from the EI incumbent, the audit log,
and the clinician report — borrowed expectations never masquerade as this
person's measured response. The GP gains per-observation noise; the real
path is arithmetically unchanged (pinned witness 13cb164c... preserved).

Governor wiring: seed_from_cohort, export_anonymized_profile, per-session
drift_status. Integration tests: cohort warm-start beats the cold 40 Hz
prior for a detuned subject; collapsed physiology flags Drifted.

Crate: 75 tests + 1 doctest. Workspace gate: 2,876 passed, 0 failed.
Benches: kNN/500 profiles ~15us, warm-start ~16us; no regression on
existing paths (recommend ~15us, calibration sweep ~111us).

https://claude.ai/code/session_01MjBucx95K4BuUxZi8NWwRH

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- **`ruview-gamma` RuVector self-learning layer (ADR-250 §10 items 3–6).** New `ruvector` module: anonymized `ProfileStore` (one-way SHA-256 hashed tags, never `person_id`; safe-session scores only), deterministic exact kNN (fixed-range normalization, index tie-break), **cohort warm-start** — a new person's optimizer is seeded from the k nearest responders as down-weighted GP pseudo-observations (`BayesianOptimizer::observe_prior`, ≥25× real-observation noise, excluded from the EI incumbent / audit / clinician report), **physiological drift detection** (Welford centroid with stimulus-input fields masked out of the distance; `Drifted` recommends re-calibration), and deterministic k-means response clustering (farthest-point seeding, no RNG). Wired into `RufloGovernor` (`seed_from_cohort`, `export_anonymized_profile`, per-session `drift_status`). The GP gains per-observation noise (real path unchanged — pinned witness `13cb164c…` preserved). 11 new module tests + 2 integration tests (cohort warm-start beats the cold 40 Hz prior for a detuned subject; collapsed physiology flags drift); crate now 75 tests + 1 doctest. Benches: kNN over 500 profiles ~15 µs, full warm-start ~16 µs; no regression on existing paths.
 - **`ruview-gamma` crate (ADR-250) — Adaptive Gamma Entrainment.** Governed, deterministic, safety-constrained personalization of 40 Hz-prior light+sound stimulation, treating 40 Hz as the evidence-based *starting prior* and learning each person's safe entrainment response curve. Eleven modules: `stimulus` (params + `SafetyEnvelope` validate/clamp), `safety` (exclusion screen + latched `SafetyMonitor` with hard-stop reasons), `response` (`RuViewState`, optional `EegMeasurement`, 20-field `PersonResponseVector` with sticky adverse flag), `objective` (safe-entrainment score; safety is a hard gate, not a weight), `simulator` (deterministic ChaCha20 `frequency_response_curve`), `optimizer` (Phase-1 calibration sweep + Phase-2 GP/Expected-Improvement + Phase-4 closed-loop control), `bandit` (Phase-3 LinUCB over envelope-safe arms), `session` (reproducible SHA-256 `session_hash`), `ruflo` (consent→exclusion→envelope→run→monitor→score→update→witnessed audit, trial/sham mode, clinician export, claim discipline), `proof` (deterministic bundle witness), `math` (dependency-light numerics). **Safety invariant** (asserted in tests): no recommendation, calibration step, bandit arm, or closed-loop nudge can ever emit a stimulus outside the `SafetyEnvelope`; non-finite inputs clamp to the conservative floor. **Claim discipline**: the only product claim is `PRODUCT_CLAIM` = "personalized entrainment optimization" — never Alzheimer's treatment (ADR-250 §19). Standalone leaf crate (no internal RuView deps), `publish = false` pending safety sign-off. 64 unit/integration tests + 1 doctest pass; deterministic witness pinned (`13cb164c…`); criterion benches (safety-stop tick ~9.3 ns vs the ADR §17 500 ms bound, Bayesian recommend ~105 µs, full 9-session governed sweep ~486 µs). See [ADR-250](docs/adr/ADR-250-adaptive-gamma-entrainment.md).
 - **RuView beyond-SOTA research series** (`docs/research/ruview-beyond-sota/`, 6 docs) — research-swarm output defining the beyond-SOTA bar and the path to it: system capability audit (role→crate maturity matrix, gap analysis, risk register), web-verified 2026 SOTA landscape per capability axis (incl. ratified IEEE 802.11bf-2025), 8-pillar target architecture on the ADR-136 contract spine (no rewrite), 6-layer benchmark/validation methodology (all 15 criterion bench targets inventoried; ADR-149 statistical protocol), and a determinism-safe optimization roadmap. Includes session validation evidence: 2,797 workspace tests / 0 failed, Python proof PASS (bit-exact), paired pre/post criterion runs.