Use shared builder for flutter builds

.gitea/workflows/build-and-deploy.yml

@@ -25,14 +25,12 @@ jobs:
       - name: Free Docker build space
         run: |
           set -euo pipefail
-          docker buildx prune --all --force || true
-          docker builder prune --all --force || true
-          docker system prune --all --force || true
+          docker buildx prune --builder builder --all --max-used-space 40gb -f || true
 
       - name: Build and push image
         run: |
           set -euo pipefail
-          builder="mapflow-builder"
+          builder="builder"
           if ! docker buildx inspect "$builder" >/dev/null 2>&1; then
             docker buildx create --name "$builder" --driver docker-container --buildkitd-config /etc/buildkit/buildkitd.toml
           fi
@@ -82,3 +80,8 @@ jobs:
             -H "x-api-key: ${{ secrets.DOKPLOY_TOKEN }}" \
             -H "Content-Type: application/json" \
             -d "$payload"
+
+      - name: Prune shared BuildKit cache
+        run: |
+          set -euo pipefail
+          docker buildx prune --builder builder --all --max-used-space 40gb -f