fix: update Docker workflow to use correct target stage name

- Change target from bolt-ai-production to runtime
- Matches the actual stage name in the new Dockerfile structure
- Fixes CI failure: target stage 'bolt-ai-production' could not be found

Author: Stijnus

.github/workflows/docker.yaml

@@ -57,7 +57,7 @@ jobs:
         with:
           context: .
           platforms: linux/amd64,linux/arm64
-          target: bolt-ai-production
+          target: runtime
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}