Management pages use the new shared application header

## Summary

Fifteen Shared UX PRs migrate page headers to the new shared AppHeader component introduced with the Chrome Next navigation. Affected pages: Maintenance windows, Reporting, Graph, Observability Overview, Saved objects, Roles, API keys, Spaces, GenAI settings, the tutorial directory (sample data), Users, Logstash pipelines, Transforms, Role mappings, and Data views. The page title, description, back link, and primary actions now render in the standard application menu at the top of the workspace, in both Classic and solution views. The sampled diff (Maintenance windows) replaces a plugin-specific PageHeader with AppHeader and drops the old Return back-link label. No new features, settings, or workflow steps are introduced.

**Why this needs docs:** These are layout-only migrations to the application header that the Kibana interface page already describes generically, so no procedure or fact changes, but screenshots of the affected management pages may now show an outdated header. Confidence stays under 0.8 because only one of the fifteen diffs was read in full and the rest is judged from PR visuals.

## Resources

- PR [#288973](https://github.com/elastic/kibana/pull/288973) — [Chrome Next] Migrate maintenance windows to AppHeader
- PR [#288979](https://github.com/elastic/kibana/pull/288979) — [Chrome Next] Migrate reporting to AppHeader
- PR [#289253](https://github.com/elastic/kibana/pull/289253) — [Chrome Next] Migrate graph to AppHeader
- PR [#288497](https://github.com/elastic/kibana/pull/288497) — [Chrome Next] Migrate o11y overview to AppHeader
- PR [#288482](https://github.com/elastic/kibana/pull/288482) — [Chrome Next] Migrate saved objects to AppHeader
- PR [#288063](https://github.com/elastic/kibana/pull/288063) — [Chrome Next] Migrate roles to AppHeader
- PR [#286866](https://github.com/elastic/kibana/pull/286866) — [Chrome Next] Migrate api keys to AppHeader
- PR [#288216](https://github.com/elastic/kibana/pull/288216) — [Chrome Next] Migrate spaces to AppHeader
- PR [#288485](https://github.com/elastic/kibana/pull/288485) — [Chrome Next] Migrate GenAI settings to AppHeader
- PR [#288673](https://github.com/elastic/kibana/pull/288673) — [Chrome Next] Migrate tutorial directory to AppHeader
- PR [#288023](https://github.com/elastic/kibana/pull/288023) — [Chrome Next] Migrate users to AppHeader
- PR [#287362](https://github.com/elastic/kibana/pull/287362) — [Chrome Next] Migrate logstash pipelines to AppHeader
- PR [#287024](https://github.com/elastic/kibana/pull/287024) — [Chrome Next] Migrate transforms to AppHeader
- PR [#288093](https://github.com/elastic/kibana/pull/288093) — [Chrome Next] Migrate role mappings to AppHeader
- PR [#287832](https://github.com/elastic/kibana/pull/287832) — [Chrome Next] Migrate data views to AppHeader

Screenshots from PR


## Availability

| Channel | Details |
|---------|---------|
| **Stack** | v9.6.0 |
| **Serverless** | Sep 7–Sep 11 |
| **Feature flag** | None — active by default |

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## If you chose to document this

[The Kibana interface](https://www.elastic.co/docs/explore-analyze/find-and-organize/kibana-interface) > Application menu
- **What the docs say:** The application menu sits at the top of the workspace and holds the actions available on the current page. When the actions don't all fit, the remaining ones move to the ellipsis More menu.
- **What to add:** No text change needed, the description already matches the AppHeader. Review-only: when refreshing screenshots for 9.6, check the pages that show a management page header (Maintenance windows, Spaces, Roles, Users, API keys, Role mappings, Data views, Transforms, Reporting, Saved objects, Graph, Logstash pipelines, GenAI settings, sample data) and flag any whose header still shows the old layout. Applies from 9.6.0 and in serverless.