fix: prevent Docker image push on pull requests

The build-and-test workflow was pushing Docker images to ghcr.io on every
pull request, which wastes registry storage and CI resources. This change
makes the push conditional so that:

- Pull requests: build and test only (no push)
- Main branch pushes: build, test, and push
- Version tags: build, test, and push
- Manual workflow dispatch: build, test, and push

This aligns with the pattern used in mission-control repository.

Author: adityathebe

.github/workflows/build-and-test.yml

@@ -55,7 +55,7 @@ jobs:
         with:
           context: .
           platforms: linux/amd64,linux/arm64
-          push: true
+          push: ${{ github.event_name != 'pull_request' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: |