feat(firmware): QEMU ESP32-S3 testing platform (ADR-061)

Implement full QEMU emulation framework for firmware testing without
physical hardware:

Mock CSI Generator (mock_csi.c):
- 10 test scenarios: empty room, static/walking person, fall, multi-person,
  channel sweep, MAC filter, ring overflow, boundary RSSI, zero-length
- Physics-based signal model with breathing modulation and Doppler
- LFSR pseudo-random noise, CONFIG_CSI_MOCK_ENABLED Kconfig guard
- Scenario 255 runs all sequentially

QEMU Runner & CI:
- qemu-esp32s3-test.sh: build, merge flash image, run QEMU, validate
- validate_qemu_output.py: 14 automated checks (boot, NVS, edge, vitals,
  crash detection) with colored output and severity-based exit codes
- generate_nvs_matrix.py: 14 NVS provisioning configs for matrix testing
- firmware-qemu.yml: GitHub Actions CI with 4-scenario matrix

Fuzz Testing:
- 3 libFuzzer targets: CSI serialize, NVS config validation, ring buffer
- Host-compilable ESP-IDF stubs (no ESP-IDF dependency for fuzzing)
- 6 seed corpus files for guided fuzzing
- Makefile with ASAN + UBSAN sanitizers

Documentation:
- firmware/esp32-csi-node/README.md: comprehensive QEMU testing guide
- Root README.md: collapsed QEMU testing section

Build verified: normal firmware build (RC=0) with mock_csi excluded.

Closes #259

Co-Authored-By: claude-flow <ruv@ruv.net>

.github/workflows/firmware-qemu.yml

@@ -0,0 +1,190 @@
+name: Firmware QEMU Tests (ADR-061)
+
+on:
+  push:
+    paths:
+      - 'firmware/**'
+      - 'scripts/qemu-esp32s3-test.sh'
+      - 'scripts/validate_qemu_output.py'
+      - 'scripts/generate_nvs_matrix.py'
+      - '.github/workflows/firmware-qemu.yml'
+  pull_request:
+    paths:
+      - 'firmware/**'
+      - 'scripts/qemu-esp32s3-test.sh'
+      - 'scripts/validate_qemu_output.py'
+      - 'scripts/generate_nvs_matrix.py'
+      - '.github/workflows/firmware-qemu.yml'
+
+env:
+  IDF_VERSION: "v5.4"
+  QEMU_REPO: "https://github.com/espressif/qemu.git"
+  QEMU_BRANCH: "esp-develop"
+
+jobs:
+  build-qemu:
+    name: Build Espressif QEMU
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cache QEMU build
+        id: cache-qemu
+        uses: actions/cache@v4
+        with:
+          path: /opt/qemu-esp32
+          key: qemu-esp32s3-${{ env.QEMU_BRANCH }}-v2
+
+      - name: Install QEMU build dependencies
+        if: steps.cache-qemu.outputs.cache-hit != 'true'
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y \
+            git build-essential ninja-build pkg-config \
+            libglib2.0-dev libpixman-1-dev libslirp-dev \
+            python3 python3-venv
+
+      - name: Clone and build Espressif QEMU
+        if: steps.cache-qemu.outputs.cache-hit != 'true'
+        run: |
+          git clone --depth 1 -b "$QEMU_BRANCH" "$QEMU_REPO" /tmp/qemu-esp
+          cd /tmp/qemu-esp
+          mkdir build && cd build
+          ../configure \
+            --target-list=xtensa-softmmu \
+            --prefix=/opt/qemu-esp32 \
+            --enable-slirp \
+            --disable-werror
+          ninja -j$(nproc)
+          ninja install
+
+      - name: Verify QEMU binary
+        run: |
+          /opt/qemu-esp32/bin/qemu-system-xtensa --version
+          echo "QEMU binary size: $(stat -c%s /opt/qemu-esp32/bin/qemu-system-xtensa) bytes"
+
+      - name: Upload QEMU artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: qemu-esp32
+          path: /opt/qemu-esp32/
+          retention-days: 7
+
+  qemu-test:
+    name: QEMU Test (${{ matrix.nvs_config }})
+    needs: build-qemu
+    runs-on: ubuntu-latest
+    container:
+      image: espressif/idf:${{ env.IDF_VERSION }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        nvs_config:
+          - default
+          - full-adr060
+          - edge-tier0
+          - tdm-3node
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Download QEMU artifact
+        uses: actions/download-artifact@v4
+        with:
+          name: qemu-esp32
+          path: /opt/qemu-esp32
+
+      - name: Make QEMU executable
+        run: chmod +x /opt/qemu-esp32/bin/qemu-system-xtensa
+
+      - name: Verify QEMU works
+        run: /opt/qemu-esp32/bin/qemu-system-xtensa --version
+
+      - name: Install Python dependencies
+        run: pip install esptool esp-idf-nvs-partition-gen
+
+      - name: Set target ESP32-S3
+        working-directory: firmware/esp32-csi-node
+        run: |
+          . $IDF_PATH/export.sh
+          idf.py set-target esp32s3
+
+      - name: Build firmware (mock CSI mode)
+        working-directory: firmware/esp32-csi-node
+        run: |
+          . $IDF_PATH/export.sh
+          idf.py \
+            -D SDKCONFIG_DEFAULTS="sdkconfig.defaults;sdkconfig.qemu" \
+            build
+
+      - name: Generate NVS matrix
+        run: |
+          python3 scripts/generate_nvs_matrix.py \
+            --output-dir firmware/esp32-csi-node/build/nvs_matrix \
+            --only ${{ matrix.nvs_config }}
+
+      - name: Create merged flash image
+        working-directory: firmware/esp32-csi-node
+        run: |
+          . $IDF_PATH/export.sh
+
+          # Determine merge_bin arguments
+          OTA_ARGS=""
+          if [ -f build/ota_data_initial.bin ]; then
+            OTA_ARGS="0xf000 build/ota_data_initial.bin"
+          fi
+
+          python3 -m esptool --chip esp32s3 merge_bin \
+            -o build/qemu_flash.bin \
+            --flash_mode dio --flash_freq 80m --flash_size 8MB \
+            0x0     build/bootloader/bootloader.bin \
+            0x8000  build/partition_table/partition-table.bin \
+            $OTA_ARGS \
+            0x20000 build/esp32-csi-node.bin
+
+          echo "Flash image size: $(stat -c%s build/qemu_flash.bin) bytes"
+
+      - name: Inject NVS partition
+        if: matrix.nvs_config != 'default'
+        working-directory: firmware/esp32-csi-node
+        run: |
+          NVS_BIN="build/nvs_matrix/nvs_${{ matrix.nvs_config }}.bin"
+          if [ -f "$NVS_BIN" ]; then
+            echo "Injecting NVS: $NVS_BIN ($(stat -c%s "$NVS_BIN") bytes)"
+            dd if="$NVS_BIN" of=build/qemu_flash.bin \
+              bs=1 seek=$((0x9000)) conv=notrunc 2>/dev/null
+          else
+            echo "WARNING: NVS binary not found: $NVS_BIN"
+          fi
+
+      - name: Run QEMU smoke test
+        env:
+          QEMU_PATH: /opt/qemu-esp32/bin/qemu-system-xtensa
+          QEMU_TIMEOUT: "60"
+        run: |
+          # Run QEMU with timeout; capture output
+          echo "Starting QEMU (timeout: ${QEMU_TIMEOUT}s)..."
+
+          timeout "$QEMU_TIMEOUT" "$QEMU_PATH" \
+            -machine esp32s3 \
+            -nographic \
+            -drive file=firmware/esp32-csi-node/build/qemu_flash.bin,if=mtd,format=raw \
+            -serial mon:stdio \
+            -no-reboot \
+            2>&1 | tee firmware/esp32-csi-node/build/qemu_output.log || true
+
+          echo "QEMU finished. Log size: $(wc -l < firmware/esp32-csi-node/build/qemu_output.log) lines"
+
+      - name: Validate QEMU output
+        run: |
+          python3 scripts/validate_qemu_output.py \
+            firmware/esp32-csi-node/build/qemu_output.log
+
+      - name: Upload test logs
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: qemu-logs-${{ matrix.nvs_config }}
+          path: |
+            firmware/esp32-csi-node/build/qemu_output.log
+            firmware/esp32-csi-node/build/nvs_matrix/
+          retention-days: 14