feat(sensing-server): body tracking platform with persistent IDs and zones

[schwarztim]

Motivation

Upstream's accepted ADR-081 (Adaptive CSI Mesh Firmware Kernel) describes the firmware vtable and is unrelated to body tracking. However, fork-side work has built a complete body-tracking platform that fits naturally with the v2/ sensing crate — persistent IDs across ticks, zone semantics, and REST APIs that downstream integrations (Home Assistant, dashboards) expect.

This PR contributes that work to upstream under a renumbered ADR (ADR-094) to avoid collision.

Changes

• NEW: v2/crates/wifi-densepose-sensing-server/src/body_tracker.rs — BodyTracker with persistent IDs, Kalman-filtered positions, zone tracking, and transition events. Self-contained: BodyCluster input type defined inline (no dependency on fork-specific spatial_pipeline module).
• NEW: docs/adr/ADR-094-body-tracking-platform.md — design decision record (renumbered from fork ADR-081 to avoid collision with upstream ADR-081 Adaptive CSI Mesh Firmware Kernel, accepted 2026-04-19)
• v2/crates/wifi-densepose-sensing-server/src/main.rs — add body_tracker module, wire BodyTracker into AppStateInner, expose tracking REST endpoints
• CHANGELOG.md — entry under [Unreleased]

API surface

• GET /api/v1/tracking/bodies — list of tracked bodies with persistent IDs, current pose hint, current zone, last-seen timestamp
• POST /api/v1/tracking/zones — set zone definitions (rectangular regions)
• GET /api/v1/tracking/zones — current zone configuration
• DELETE /api/v1/tracking/zones/{name} — remove a named zone

Design notes

• Bodies are matched across ticks via greedy nearest-neighbor assignment on centroid distance (< 2m threshold); IDs persist until quality decays to 0 (20 absent frames at default settings)
• Simple Kalman filter (alpha=0.3 position correction + velocity estimation) smooths frame-to-frame centroid noise
• Zone events fire on tick boundaries when a body's containing zone changes
• This platform is the foundation for several upcoming PRs (activity history, fall detection, sleep detection, dashboard floor plan)

Test results

• cargo test --workspace --no-default-features: 1647 passed, 0 failed (5 unit tests in body_tracker module: creation, ID persistence, timeout decay, zone containment, zone transitions)
• python v1/data/proof/verify.py: VERDICT: FAIL — pre-existing on origin/main (numpy/scipy version drift); not caused by this PR