ci: tighten docker maintenance window and fix yaml syntax

.gitea/workflows/deploy.yml

@@ -42,12 +42,12 @@ jobs:
     container:
       image: catthehacker/ubuntu:act-latest
     steps:
-      - name: 🧹 Cleanup disk space
+      - name: 🧹 Maintenance (High Density Cleanup)
         shell: bash
         run: |
-          echo "🧹 Cleaning up dangling Docker images and stale build cache..."
-          docker system prune -f --filter "until=24h"
-          docker image prune -f --filter "dangling=true"
+          echo "Purging old build layers and dangling images..."
+          docker image prune -f
+          docker builder prune -f --filter "until=6h"
 
       - name: Checkout repository
         uses: actions/checkout@v4