fix(ci): pip3 in IDF container + fix swarm QEMU artifact path

QEMU Test jobs: espressif/idf:v5.4 container has pip3, not pip.
Swarm Test: use /opt/qemu-esp32 (fixed path) instead of
${{ github.workspace }}/qemu-build which resolves incorrectly
inside Docker containers.

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

.github/workflows/firmware-qemu.yml

@@ -114,7 +114,7 @@ jobs:
         run: /opt/qemu-esp32/bin/qemu-system-xtensa --version
 
       - name: Install Python dependencies
-        run: pip install esptool esp-idf-nvs-partition-gen
+        run: pip3 install esptool esp-idf-nvs-partition-gen
 
       - name: Set target ESP32-S3
         working-directory: firmware/esp32-csi-node
@@ -318,13 +318,13 @@ jobs:
         uses: actions/download-artifact@v4
         with:
           name: qemu-esp32
-          path: ${{ github.workspace }}/qemu-build
+          path: /opt/qemu-esp32
 
       - name: Make QEMU executable
-        run: chmod +x ${{ github.workspace }}/qemu-build/bin/qemu-system-xtensa
+        run: chmod +x /opt/qemu-esp32/bin/qemu-system-xtensa
 
       - name: Install Python dependencies
-        run: pip install pyyaml esptool esp-idf-nvs-partition-gen
+        run: pip3 install pyyaml esptool esp-idf-nvs-partition-gen
 
       - name: Build firmware for swarm
         working-directory: firmware/esp32-csi-node
@@ -342,7 +342,7 @@ jobs:
       - name: Run swarm smoke test
         run: |
           python3 scripts/qemu_swarm.py --preset ci_matrix \
-            --qemu-path ${{ github.workspace }}/qemu-build/bin/qemu-system-xtensa \
+            --qemu-path /opt/qemu-esp32/bin/qemu-system-xtensa \
             --output-dir build/swarm-results
         timeout-minutes: 10