docs: import hardware photos + sensor inventory

9 photos of the additional sensor/antenna hardware staged for ADR-120+
experimentation (captured 2026-05-18):

  sensor_01  5× u.FL pigtail antennas (bare)
  sensor_02  4× flat PCB-strip 2.4 GHz antennas w/ 3M backing + u.FL
  sensor_03  HLK-LD2402 24 GHz mmWave radar (close-up, chip S1KM0008)
  sensor_04  CP2102 USB-to-UART bridge (AMS1117-3.3 LDO)
  sensor_05  HLK-LD2402 + USB-UART wired together (working setup)
  sensor_06  ESP32-S3 dev board with microSD slot (back)
  sensor_07  ESP32-S3-WROOM with OV-camera + ribbon FFC mounted
  sensor_08  YD-ESP32-23 2022-V1.3 (back) — spare matching nodes 1-6
  sensor_09  YD-ESP32-23 (front) — ESP32-S3-N16R8 + FTDI

assets/sensors/README.md catalogues each photo + suggests where each
piece fits in the roadmap:
  * u.FL antennas → attach to n1/n5 (near-AP, sep_ratio ~0.05 per ADR-118)
  * HLK-LD2402 → vitals ground-truth reference for WiFi pipeline
  * Camera-ESP32-S3 → on-device camera capture for WiFlow Pack E.2 retrain
  * YD-ESP32-23 spare → flashable as node 7 when needed

Photos referenced only from this README, not used by any code path.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

assets/sensors/README.md

@@ -0,0 +1,42 @@
+# Sensor & antenna hardware inventory
+
+Photos of the additional sensor + antenna hardware staged for ADR-120+
+experimentation in this deployment. Captured 2026-05-18.
+
+| File | What it is | Role |
+|---|---|---|
+| [`sensor_01.jpeg`](sensor_01.jpeg) | 5× u.FL (IPEX-1) pigtail antennas, bare cable | External antenna feed for ESP32-S3 boards that have a u.FL connector but currently use the on-PCB chip antenna. Adds gain + diversity once attached. |
+| [`sensor_02.jpeg`](sensor_02.jpeg) | 4× flat PCB-strip antennas (2.4 GHz, FR4 copper trace, 3M double-sided tape backing) + u.FL pigtails | Stick-on external antennas — better gain than the chip antenna, doubles as polarisation diversity if mounted perpendicular to one another. |
+| [`sensor_03.jpeg`](sensor_03.jpeg) | **HLK-LD2402** 24 GHz mmWave radar module (V1.0, chip `S1KM0008` 2438 batch), TX/RX patch antennas, UART output | New modality. mmWave gives sub-mm range to a moving target — useful for vital-sign disambiguation alongside WiFi CSI. UART @ 256000 8N1. |
+| [`sensor_04.jpeg`](sensor_04.jpeg) | CP2102 USB-to-UART bridge (AMS1117-3.3 LDO, USB-A) | Powers + reads the HLK-LD2402 from a Mac/Linux host. Pin map: GND / RXT / TXD / 3.3V / RTS / CTS. |
+| [`sensor_05.jpeg`](sensor_05.jpeg) | The two boards from `sensor_03` + `sensor_04` wired together | Working HLK-LD2402 setup ready to receive on a USB tty (no firmware needed — module ships with its own factory firmware). |
+| [`sensor_06.jpeg`](sensor_06.jpeg) | Back of ESP32-S3 dev board with **microSD slot**, marked "Camera / SD Card / PSRAM", dual USB-UART + USB-OTG | Different board family from the 6 already in service. SD slot + USB-OTG + on-board camera connector make it a candidate for **on-device camera ground-truth capture** (alternative to using the Mac webcam for ADR-079 / Pack E.2 retraining). |
+| [`sensor_07.jpeg`](sensor_07.jpeg) | ESP32-S3-WROOM with **OV-camera mounted** + camera ribbon FFC connector | Same board family as `sensor_06`. Camera ribbon already attached. With WiFi CSI + onboard camera in one device, this could collect synchronised paired data (CSI + image) entirely without involving the Mac — the missing piece for the wiflow fine-tune Pack E.2. |
+| [`sensor_08.jpeg`](sensor_08.jpeg) | Back of **YD-ESP32-23 2022-V1.3 (V2356)** dev board | Same board family as the 6 currently provisioned (nodes 1-6). Spare. |
+| [`sensor_09.jpeg`](sensor_09.jpeg) | Front of **YD-ESP32-23**: ESP32-S3-N16R8 WiFi+BT module, FTDI USB-serial, RGB LED, dual USB-C | Confirms it's the **same hardware** we flashed for nodes 3-6 (FT232R serial chip on board, see `/dev/cu.usbserial-A5069RR4` during provisioning). |
+
+## Suggested next moves
+
+* **u.FL antennas (`sensor_01`/`_02`)** — attach to the two
+  "near-AP" nodes (n1, n5) which currently sit at sep_ratio ~0.05 per
+  the ADR-118 audit. External antenna oriented perpendicular to the
+  body axis should pull more body modulation into the signal.
+* **HLK-LD2402 mmWave (`sensor_03`–`05`)** — start as a **vitals
+  ground-truth reference** for the WiFi pipeline. Connect via the
+  USB-UART, log breathing rate at the same time as the WiFi vitals
+  detector, compare. Later fuse via `MultistaticFuser` if accuracy
+  improves materially (would warrant a fresh ADR).
+* **Camera-bearing ESP32-S3 (`sensor_06`/`_07`)** — the cleanest path
+  to Pack E.2 (WiFlow camera-supervised retrain): collect synced
+  `(CSI, MediaPipe keypoints)` pairs entirely on-device. Avoids the
+  awkward "laptop is the camera AND the server AND in the sensing
+  zone" problem from the earlier session.
+* **Spare YD-ESP32-23 (`sensor_08`/`_09`)** — flash with the same
+  build + `provision.py --node-id 7` if/when a 7-node deployment is
+  desired. Bring-up is 5 min per the ADR-117 OTA recipe.
+
+---
+
+These are reference photos only — not used by any code path. Linked
+from `docs/use-cases.md` and `CHECKLIST.md` Deferred section so future
+sessions can see the available hardware at a glance.