chore(ci): remove docker/setup-buildx-action step

BuildKit is enabled by default on ubuntu-latest runners.

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

.github/workflows/ci.yml

@@ -51,11 +51,6 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-        with:
-          driver: docker
-
       - name: Build images
         run: docker compose -f cicd/docker/docker-compose.yml build