feat: add Docker cleanup step to CI pipeline

Automatically prune unused containers, images and build cache after
each CI run to prevent disk space exhaustion on the runner.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/deploy.yaml

@@ -226,3 +226,13 @@ jobs:
                 \"run_url\": \"https://gitea.airlabs.art/${{ github.repository }}/actions/runs/${{ github.run_number }}\"
               }
             }" || true
+
+      # ===== Cleanup: remove unused Docker resources =====
+      - name: Docker Cleanup
+        if: always()
+        run: |
+          docker container prune -f
+          docker image prune -a -f
+          docker builder prune -a -f
+          echo "Disk usage after cleanup:"
+          df -h / | tail -1