Reuse canonical YAML examples in website documentation

**What would you like to be cleaned**: Avoid duplicating Kubernetes YAML manifests across Markdown pages. Add a Hugo `include` shortcode and render documentation snippets from canonical sample files, such as files under `config/samples` or `site/static/examples`. Suggested scope: - Add an `include` shortcode for YAML examples. - Select one canonical location for runnable samples. - Migrate repeated LWS and DisaggregatedSet snippets incrementally. - Make the site build fail when an included example is missing. Prior art: - [JobSet include shortcode](https://github.com/kubernetes-sigs/jobset/blob/main/site/layouts/shortcodes/include.html) - [JobSet documentation usage](https://github.com/kubernetes-sigs/jobset/blob/main/site/content/en/docs/tasks/failure_policy.md) - [Kueue include shortcode](https://github.com/kubernetes-sigs/kueue/blob/main/site/layouts/shortcodes/include.html) **Why is this needed**: Copied YAML can drift from the CRD schema and runnable examples. Review of #989 highlighted how repeated DisaggregatedSet snippets can diverge from the required `roles[].spec` structure. Using a single source of truth reduces maintenance, applies fixes consistently, and allows CI to validate the same manifests shown in the documentation.