Merge #491: feat(sensing-server): adaptive person count — RollingP95 + dedup_factor runtime API

Integrating @schwarztim's PR #491 into main on their behalf — their fork has
fallen too far behind for a clean rebase (the PR's commit graph dropped
silently during `git rebase origin/main`), so applying as a merge from the
fork head to preserve the diff cleanly.

What this lands:
- `RollingP95` adaptive normaliser for the person-count feature scaling.
  Streaming P95 over a 600-sample / ~30 s sliding window. Cold-start
  (<60 samples) falls back to the legacy denominators (variance/300,
  motion_band_power/250, spectral_power/500) so day-0 behaviour is
  preserved on every deployment.
- `RuntimeConfig` struct + `load_runtime_config` / `save_runtime_config`
  persisted to `data/config.json`. Exposes `dedup_factor` via REST so
  multi-node deployments can tune cluster-deduplication without a rebuild,
  including an auto-tune endpoint that derives optimal dedup from a known
  person count (calibration mode).
- `compute_person_score()` now takes &AppStateInner alongside &FeatureInfo
  so the adaptive denominators are reachable. All 3 call sites updated.
- New `AppStateInner` fields: `p95_variance`, `p95_motion_band_power`,
  `p95_spectral_power`, `dedup_factor`, `data_dir`.

Closes #491. Directly addresses:
- #499 (double skeletons, multi-node) — the slot-clustering problem this
  PR's adaptive normaliser was designed to fix
- #519 Bug 1 (ghost person detection on edge-tier 1 & 2 multi-node)
- #496 (person count over-reporting on single-room single-person)

Verified locally:
- cargo check -p wifi-densepose-sensing-server --no-default-features: 1.0s
- cargo test -p wifi-densepose-sensing-server --no-default-features --lib:
  233/233 passed in 25.0s

Co-authored-by: @schwarztim
Co-Authored-By: claude-flow <ruv@ruv.net>

CHANGELOG.md

@@ -144,6 +144,22 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **README: corrected the camera-supervised pose-accuracy claim** (audit finding #5; see PR #535) — "92.9% PCK@20" → the ADR-079 target (35%+; proxy baseline 35.3%), noting P7/P8/P9 are pending.
 
 ### Added
+- **`RollingP95` adaptive feature normalizer** (`v2/crates/wifi-densepose-sensing-server`) —
+  Streaming P95 estimator (600-sample / ~30 s sliding window) that self-calibrates
+  feature normalization to whatever distribution the deployment produces. Replaces
+  fixed-scale denominators (`variance/300`, `motion/250`, `spectral/500`) which saturated
+  when live ESP32 values exceeded those limits, collapsing dynamic range to zero.
+  Cold-start (<60 samples) falls back to the legacy denominators so day-0 behaviour
+  is preserved. Deployment-neutral: no hardcoded values. (ADR-044 §5.2)
+
+- **`dedup_factor` runtime configuration API** (`v2/crates/wifi-densepose-sensing-server`) —
+  Exposes the multi-node person-count deduplication divisor at runtime via REST:
+  - `GET  /api/v1/config/dedup-factor` — read current value.
+  - `POST /api/v1/config/dedup-factor` — set value (clamped 1.0–10.0, persisted).
+  - `POST /api/v1/config/ground-truth` — auto-tunes `dedup_factor` from a known
+    person count (`{"count": N}`); derives optimal divisor from current node-sum.
+  Config is persisted to `data/config.json` and reloaded on restart. (ADR-044 §5.3)
+
 - **`nvsim` crate — deterministic NV-diamond magnetometer pipeline simulator** (ADR-089) —
   New standalone leaf crate at `v2/crates/nvsim` modeling a forward-only
   magnetic sensing path: scene → source synthesis (Biot–Savart, dipole,