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.

.github/workflows/firmware-ci.yml

@@ -38,7 +38,7 @@ jobs:
           echo "version.txt matches the release tag."
 
   build:
-    name: Build ESP32-S3 Firmware (${{ matrix.variant }})
+    name: Build firmware (${{ matrix.target }} / ${{ matrix.variant }})
     runs-on: ubuntu-latest
     container:
       image: espressif/idf:v5.4
@@ -47,17 +47,27 @@ jobs:
       matrix:
         include:
           - variant: 8mb
+            target: esp32s3
             sdkconfig: sdkconfig.defaults
             partition_table_name: partitions_display.csv
             size_limit_kb: 1100
             artifact_app: esp32-csi-node.bin
             artifact_pt: partition-table.bin
           - variant: 4mb
+            target: esp32s3
             sdkconfig: sdkconfig.defaults.4mb
             partition_table_name: partitions_4mb.csv
             size_limit_kb: 1100
             artifact_app: esp32-csi-node-4mb.bin
             artifact_pt: partition-table-4mb.bin
+          # ADR-110: ESP32-C6 research target (Wi-Fi 6 / 802.15.4 / TWT / LP-core)
+          - variant: c6-4mb
+            target: esp32c6
+            sdkconfig: sdkconfig.defaults
+            partition_table_name: partitions_4mb.csv
+            size_limit_kb: 1100
+            artifact_app: esp32-csi-node-c6.bin
+            artifact_pt: partition-table-c6.bin
 
     steps:
       - uses: actions/checkout@v4
@@ -66,12 +76,22 @@ jobs:
         working-directory: firmware/esp32-csi-node
         run: |
           . $IDF_PATH/export.sh
-          if [ "${{ matrix.variant }}" != "8mb" ]; then
+          # 4mb variant supplies its own sdkconfig.defaults overlay.
+          # c6-4mb variant relies on the auto-applied sdkconfig.defaults.esp32c6
+          # overlay (ESP-IDF auto-loads sdkconfig.defaults.$TARGET when present).
+          if [ "${{ matrix.variant }}" = "4mb" ]; then
             cp "${{ matrix.sdkconfig }}" sdkconfig.defaults
           fi
-          idf.py set-target esp32s3
+          idf.py set-target ${{ matrix.target }}
           idf.py build
 
+      - name: Build and run host-side ADR-110 unit tests
+        if: matrix.variant == 'c6-4mb'
+        working-directory: firmware/esp32-csi-node/test
+        run: |
+          make test_adr110
+          ./test_adr110
+
       - name: Verify binary size (< ${{ matrix.size_limit_kb }} KB gate)
         working-directory: firmware/esp32-csi-node
         run: |