Free runner disk before Docker publish

The multi-platform Docker publish job can exhaust the hosted runner disk before BuildKit finishes, causing ENOSPC failures during log writing and cleanup.

Remove unused hosted toolchains and stale local Docker data before QEMU and Buildx setup so release builds have more room without changing Docker image inputs or install scripts.

.github/workflows/docker-publish.yml

@@ -108,6 +108,27 @@ jobs:
             exit 1
           fi
 
+      - name: Free runner disk space
+        run: |
+          echo "Disk before cleanup:"
+          df -h /
+          docker system df || true
+
+          sudo rm -rf \
+            /opt/az \
+            /opt/ghc \
+            /opt/hostedtoolcache/CodeQL \
+            /usr/local/.ghcup \
+            /usr/local/lib/android \
+            /usr/local/share/boost \
+            /usr/share/dotnet
+          sudo apt-get clean
+          docker system prune -af --volumes || true
+
+          echo "Disk after cleanup:"
+          df -h /
+          docker system df || true
+
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v3