Streamline the CI and release workflows:
- ci.yaml is now PR-only (no push-to-main re-run) and keeps only lint and
dependency-review; the gateway-image local build/smoke job is removed.
- Split the path-sensitive jobs into ci-python.yaml and ci-manifests.yaml,
each using native on.pull_request.paths filtering so unrelated PRs skip them.
- Drop the duplicate check-manifests.py run from the lint job.
- release.yaml: skip the tests job steps for tags already on main (where PR CI
already ran), keeping them only for release-branch tags.
Co-authored-by: SREDevOpsAgents <agents@sredevops.org>
