fix: use docker build --push for buildx container driver

Docker buildx with docker-container driver doesn't load images
into the local daemon. Use --push to push directly during build.

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

.gitea/workflows/ci.yml

@@ -80,6 +80,4 @@ jobs:
         run: |
           TAG="harbor.mymx.me/library/bouncer:${GITHUB_SHA::8}"
           LATEST="harbor.mymx.me/library/bouncer:latest"
-          docker build -t "$TAG" -t "$LATEST" -f Containerfile .
-          docker push "$TAG"
-          docker push "$LATEST"
+          docker build --push -t "$TAG" -t "$LATEST" -f Containerfile .