Migrate workflows to Blacksmith (#16)

Co-authored-by: blacksmith-sh[bot] <157653362+blacksmith-sh[bot]@users.noreply.github.com>

Author: blacksmith-sh[bot]

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ concurrency:
 
 jobs:
   docker:
-    runs-on: ubuntu-latest
+    runs-on: blacksmith-4vcpu-ubuntu-2404
     env:
       POSTGRES_USER: duopus
       POSTGRES_PASSWORD: ci
@@ -33,8 +33,8 @@ jobs:
         working-directory: backend
         run: uv sync --locked --extra dev && uv run pytest
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
+      - name: Setup Blacksmith Builder
+        uses: useblacksmith/setup-docker-builder@v1
 
       - name: Build Compose images
         run: docker compose build