Docs: Tree example

[madsrasmussen]

This PR adds a basic "Tree Example" to the examples folder.

The examples include:

• Tree + Tree Item Registration
• Tree Repository + Store Registration
• A Dashboard to show how to render a tree anywhere in the backoffice
• How to use the tree in the sidebar menu

[Copilot]

Pull Request Overview

This PR introduces a basic "Tree Example" demonstrating how to register a tree, implement its associated repository and store, and integrate a dashboard and sidebar menu to render the tree in the backoffice. Key changes include:

• New TypeScript interfaces to define tree item and root models.
• Implementation of tree store, repository, and local data source functionality.
• Addition of manifests and a dashboard element to integrate the tree with the backoffice and menu.

Reviewed Changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Umbraco.Web.UI.Client/examples/tree/tree/types.ts	Defines tree item and tree root models.
src/Umbraco.Web.UI.Client/examples/tree/tree/manifests.ts	Registers tree and tree item manifests with proper entity types.
src/Umbraco.Web.UI.Client/examples/tree/tree/data/store/*.ts	Introduces tree store, context token, and corresponding manifests.
src/Umbraco.Web.UI.Client/examples/tree/tree/data/repository/*.ts	Implements a tree repository using a local data source.
src/Umbraco.Web.UI.Client/examples/tree/tree/data/local-data-source/tree.local.data-source.ts	Provides a local data source with methods to retrieve root items, children, and ancestors.
src/Umbraco.Web.UI.Client/examples/tree/dashboard-with-tree/*.ts	Adds a dashboard element and manifest for visual rendering of the tree.
Remaining files	Set up necessary constants, entities, and index exports to integrate the example.