ci: add automated image cleanup

Automatically cleanup old images when a new build is pushed.

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

.github/workflows/image.yml

@@ -44,3 +44,15 @@ jobs:
             ghcr.io/${{ github.repository }}:${{ github.sha }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
+
+  cleanup:
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - name: Delete old images
+        uses: actions/delete-package-versions@v5
+        with:
+          package-name: ${{ github.event.repository.name }}
+          package-type: 'container'
+          min-versions-to-keep: 3
+          ignore-versions: '^latest$'