Solution navigation menus get solution-specific landing items instead of a generic Home

## Summary

The solution navigation menu no longer forces a generic Home item at the top of every solution. Each solution now decides its landing item: Search, Workplace AI, and Vector DB keep Home. Observability shows Overview with a home icon, and on serverless falls back to Get started (rocket icon) when the Overview page is unavailable. Security (Elastic Stack, serverless, and Elastic AI SOC Engine) removes the primary Home item because it duplicated the Launchpad and the Get started link in the menu footer. The Elastic logo now opens the default route setting of the space rather than the navigation home node.

**Why this needs docs:** Navigation labels changed in a user-visible way (Home becomes Overview in Observability, Home disappears from Security), and while the Kibana interface, Security UI, and Customize navigation pages contain no statement that becomes wrong, solution docs and nav screenshots that reference a Home menu item were not exhaustively searched, so a targeted review is warranted.

## Resources

- PR [#287690](https://github.com/elastic/kibana/pull/287690) — Remove renderAs home from solution navigation

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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## Suggested edits

[The Kibana interface](https://www.elastic.co/docs/explore-analyze/find-and-organize/kibana-interface) > Navigation menu
- **What the docs say:** The navigation menu lists the apps of your solution view. When a top-level item contains sub-items, selecting it opens the secondary navigation to its right.
- **What to add:** Review-only across docs-content: search the Observability and Security solution docs for procedures that start from a Home item in the navigation menu (for example select Home in the navigation menu, or Observability → Home) and for navigation screenshots that show Home as the first item. In Observability the first item is now Overview (or Get started on serverless projects without the Overview page). In Security the primary Home item is gone and Get started remains in the menu footer. Search projects keep Home. Preserve pre-9.6 wording with a stack tag where a procedure named Home. Applies from 9.6.0 and in serverless.