ci: prune old build-NNN images and stale build cache after deploy

Old build-NNN tags accumulated in the shared host /var/lib/docker
(~1.3GB each, 24 builds = ~30GB) and filled the disk to 100%.
Keep the newest 5 build tags, drop dangling images, and prune build
cache older than 72h on every run.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/deploy.yaml

@@ -56,3 +56,23 @@ jobs:
           curl -sf \
             "http://coolify:8080/api/v1/deploy?uuid=gyjo0mtw2c42ej3xxvbz8zio&force=true" \
             -H "Authorization: Bearer ${{ secrets.COOLIFY_TOKEN }}"
+
+      - name: Prune old build images and cache
+        if: always()
+        run: |
+          BASE="${{ env.REGISTRY }}/${{ env.IMAGE }}"
+          KEEP=5
+          # Keep the newest $KEEP build-NNN tags; remove the rest.
+          # The build daemon is the shared host daemon, so these images
+          # otherwise accumulate in /var/lib/docker (~1.3GB each).
+          docker images "${BASE}" --format '{{.Tag}}' \
+            | grep -E '^build-[0-9]+$' \
+            | sort -t- -k2 -nr \
+            | tail -n +$((KEEP + 1)) \
+            | while read -r tag; do
+                echo "🗑️  Removing ${BASE}:${tag}"
+                docker rmi "${BASE}:${tag}" || true
+              done
+          # Dangling images + build cache older than 72h (keeps recent layers warm)
+          docker image prune -f || true
+          docker builder prune -f --filter 'until=72h' || true