feat(privshield): E2E hardware program — validated C core + multi-provider firmware scaffolds

Take VEIL from the synthetic Rust reference model toward real WiFi silicon
across multiple hardware providers, around one shared, host-validated core.
Answers the questions "can OpenWRT / open WiFi software implement this?" and
"can ESP32 help scramble signals?" with an honest per-platform feasibility map.

Portable C shield core (firmware/privshield/core/) — VALIDATED (host test):
- veil_shield.{h,c}: keyed Givens-rotation obfuscation of the identity-bearing
  "fine" subspace, C99, no malloc / no libc I/O, only <math.h>. SplitMix64 key
  schedule byte-identical to the Rust crate, so on-air behavior is consistent
  everywhere and every adapter links the same math.
- make test passes: energy conservation (orthogonal => "not jamming"),
  reversibility (recover inverts apply), wrong-key-fails, and PRNG stream parity
  with the Rust crate. This is build/host evidence, NOT silicon.

Per-provider adapters (all SYNTHETIC / L0, build-only, TODO(hw) markers):
- openwifi/  grade B (ceiling A, effort D): only open PHY/MAC (FPGA) that can
  host the full keyed rotation + inverse; needs new HDL + 2nd TX chain. Carries
  the P5 measurement protocol (MEASUREMENT.md) for the first MEASURED result.
- openwrt/   grade C: per-packet keyed unitary is blob-blocked on commodity APs;
  coarse compliant knobs (TX antenna map, sounding-cadence jitter) reachable
  from userspace/hostapd; ath9k is the one credible driver-patch route.
- nexmon/    grade C: reading the compressed-BF angles is solved (nexmon_csi /
  Wi-BFI); shaping the transmitted report is research-grade (D11 ucode-adjacent).
- esp32/     grade F (self) / B (supporting): cannot shape its own BF feedback
  (closed esp-phy-lib blob); legitimate as a sensing detector and external-RIS
  controller — the honest way ESP32 "helps scramble", via an external surface.

Docs:
- firmware/privshield/README.md: architecture, layout, and the feasibility matrix.
- ADR-290: the E2E hardware program, PROOF discipline, and per-provider decision;
  added to docs/adr/README.md index.

Compliant waveform controls only, never jamming. No adapter has run on silicon;
no MEASURED claim is made (that is roadmap P5, gated on a captured log).

Co-Authored-By: claude-flow <ruv@ruv.net>
Claude-Session: https://claude.ai/code/session_01WEXNqzs7UsfNFBcP5yW21p

docs/adr/README.md

@@ -147,6 +147,7 @@ Statuses: **Proposed** (under discussion), **Accepted** (approved and/or impleme
 | [ADR-286](ADR-286-wifi-densepose-sar-harness-via-metaharness.md) | `wifi-densepose-sar-harness` — MetaHarness with darwin/router/flywheel | Accepted (implemented, published) |
 | [ADR-288](ADR-288-veil-privacy-shield-compliant-waveform.md) | VEIL — compliant-waveform privacy shield against unauthorized WiFi sensing (`wifi-densepose-privshield`) | Proposed (implemented, P1 reference) |
 | [ADR-289](ADR-289-wifi-densepose-privshield-harness-via-metaharness.md) | `wifi-densepose-privshield-harness` — npm MetaHarness for the VEIL crate (guidance/router/flywheel) | Proposed (implemented, P1) |
+| [ADR-290](ADR-290-veil-e2e-hardware-implementation-program.md) | VEIL end-to-end hardware implementation program — portable C core + multi-provider firmware scaffolds (openwifi/openwrt/nexmon/esp32) | Proposed (P4 scaffolding; C core host-validated) |
 
 ---