ADR-110: ESP32-C6 firmware extension (#764)

Closes the firmware-side ADR-110 design at v0.7.0-esp32 after a 38-iter /loop SOTA sprint.

Headline (bench, COM9+COM12 ESP32-C6):
- 99.56% cross-board RX, 104.1 µs smoothed offset stdev (≤100 µs §2.4 target met)
- 3.95× EMA suppression, 1.4 ppm crystal skew preserved

4 firmware releases: v0.6.7 / v0.6.8 / v0.6.9 / v0.7.0-esp32.
42 ADR-110 unit tests, 1761 v2 workspace tests, full Firmware CI + QEMU green.

README.md

@@ -80,7 +80,7 @@ docker pull ruvnet/wifi-densepose:latest
 docker run -p 3000:3000 ruvnet/wifi-densepose:latest
 # Open http://localhost:3000
 
-# Option 2: Live sensing with ESP32-S3 hardware ($9)
+# Option 2a: Live sensing with ESP32-S3 hardware ($9)
 # Flash firmware, provision WiFi, and start sensing:
 python -m esptool --chip esp32s3 --port COM9 --baud 460800 \
   write_flash 0x0 bootloader.bin 0x8000 partition-table.bin \
@@ -88,6 +88,20 @@ python -m esptool --chip esp32s3 --port COM9 --baud 460800 \
 python firmware/esp32-csi-node/provision.py --port COM9 \
   --ssid "YourWiFi" --password "secret" --target-ip 192.168.1.20
 
+# Option 2b: WiFi 6 + 802.15.4 research sensing with ESP32-C6 ($6-10, ADR-110)
+# Same csi-node firmware compiled for the C6 target — picks up the C6
+# overlay (sdkconfig.defaults.esp32c6) automatically.
+cd firmware/esp32-csi-node
+idf.py set-target esp32c6 && idf.py build
+idf.py -p COM6 flash
+# C6 boot extras (vs S3): HE-LTF subcarrier tagging in ADR-018 bytes 18-19,
+#   802.15.4 mesh time-sync on channel 15, TWT setup when the AP supports it,
+#   opt-in LP-core wake-on-motion for ~5 µA battery seed nodes.
+# v0.6.7 adds: real LP-core RISC-V motion-gate program (debounce + motion
+#   counter) and a Wi-Fi 6 soft-AP with TWT Responder so two C6 boards can
+#   benchmark real iTWT without buying an 11ax router. Both default off,
+#   flip CONFIG_C6_{LP_CORE,SOFTAP_HE}_ENABLE to turn them on.
+
 # Option 3: Full system with Cognitum Seed ($140)
 # ESP32 streams CSI → bridge forwards to Seed for persistent storage + kNN + witness chain
 node scripts/rf-scan.js --port 5006           # Live RF room scan
@@ -103,7 +117,8 @@ node scripts/mincut-person-counter.js --port 5006  # Correct person counting
 > | Option | Hardware | Cost | Full CSI | Capabilities |
 > |--------|----------|------|----------|-------------|
 > | **ESP32 + Cognitum Seed** (recommended) | ESP32-S3 + [Cognitum Seed](https://cognitum.one) | ~$140 | Yes | Presence, motion, breathing, heart rate, fall detection, multi-person counting, 17-keypoint pose (signed Cog binary), 105-cog catalog, persistent vector store, kNN search, witness chain, MCP proxy |
-> | **ESP32 Mesh** | 3-6x ESP32-S3 + WiFi router | ~$54 | Yes | Same capabilities as above without the persistent-memory features |
+> | **ESP32 Mesh** | 3-6× ESP32-S3 + WiFi router | ~$54 | Yes | Same capabilities as above without the persistent-memory features |
+> | **ESP32-C6 research node** ([ADR-110](docs/adr/ADR-110-esp32-c6-firmware-extension.md), [witness](docs/WITNESS-LOG-110.md), [reviewer guide](docs/ADR-110-REVIEW-GUIDE.md), [firmware v0.7.0](https://github.com/ruvnet/RuView/releases/tag/v0.7.0-esp32)) | ESP32-C6-DevKit ($6–10) | ~$10 | Yes (Wi-Fi 6 capable) | Same CSI pipeline as S3 with the dual-target firmware. **Firmware-side ADR-110 substrate now closed** (v0.7.0): ESP-NOW cross-board mesh quantified at **99.56 % match / 104 µs smoothed offset stdev / 3.95× EMA suppression** over a 5-min two-board soak (witness §A0.10), 32-byte UDP sync packet with operator-tunable cadence (§A0.12), ADR-018 byte 19 bit 4 wire-fix sourced from the working ESP-NOW path (§A0.13). Wire format ready for HE-LTF PPDU tagging in ADR-018 bytes 18-19 (firmware encoder + Rust + Python decoders verified end-to-end across 23 unit tests). LP-core motion-gate RISC-V program and Wi-Fi 6 soft-AP with TWT Responder both ship as opt-in code paths (default off). **Hardware-gated for measurement**: HE-LTF live subcarrier capture needs an 11ax AP (IDF v5.4 doesn't expose AP-side HE config — §A0.6); ~5 µA LP-core hibernation needs an INA meter to capture; 802.15.4 raw RX is broken in IDF v5.4 (workaround: ESP-NOW transport, shipped + measured). See witness log for the empirical / claimed split. |
 > | **Research NIC** | Intel 5300 / Atheros AR9580 | ~$50-100 | Yes | Full CSI with 3x3 MIMO |
 > | **Any WiFi** | Windows, macOS, or Linux laptop | $0 | No | RSSI-only: coarse presence and motion (see [tutorial #36](https://github.com/ruvnet/RuView/issues/36)) |
 >