Delete multi-arch manifest tag on branch deletion

The cleanup job was only deleting arch-specific tags (branch-amd64,
branch-arm64) but not the multi-arch manifest tag (branch). Now
deletes all three tags when a branch is deleted.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dpark01

.github/workflows/docker.yml

@@ -167,8 +167,8 @@ jobs:
           # Sanitize branch name (same logic as build jobs)
           SUFFIX=$(echo '${{ github.event.ref }}' | tr '/' '-')
 
-          for arch in amd64 arm64; do
-            TAG="${SUFFIX}-${arch}"
+          # Delete multi-arch manifest and arch-specific images
+          for TAG in "${SUFFIX}" "${SUFFIX}-amd64" "${SUFFIX}-arm64"; do
             echo "Looking for tag: $TAG"
 
             # Get version ID for this tag