CI: docker image prune nach jedem Deploy

Entfernt dangling/orphan Images automatisch nach docker pull + deploy.
Verhindert dass sich alte untagged Images ansammeln (~533MB pro Build).

[skip ci]

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitlab-ci.yml

@@ -170,6 +170,8 @@ deploy:
         -v /mnt/cache/appdata/dockge/container/jukebox/sounds/:/data/sounds:rw \
         "$DEPLOY_IMAGE"
     - docker ps --filter name="$CONTAINER_NAME" --format "ID={{.ID}} Status={{.Status}} Image={{.Image}}"
+    - echo "[Deploy] Cleaning up dangling images..."
+    - docker image prune -f || true
 
 deploy-nightly:
   stage: deploy