Replace Contentment picker with native block picker for In Page Navigation

[deanleigh]

Summary

The In Page Navigation feature currently uses Contentment v6.1.1 Data List with a custom IContentmentDataSource (FeatureBlockDataSource) to let editors pick which blocks appear in the navigation. This requires:

• Contentment package dependency
• Custom DataSource class
• EnableBuffering() middleware for the Contentment API path
• Workarounds for GetCurrentContentId() returning 0 in Umbraco 17

Umbraco's native block grid already has a block picker UI using uui-combobox (see umb-property-editor-ui-block-grid-area-type-permission). We should investigate replacing the Contentment approach with the native picker component.

Benefits

• Remove Contentment package dependency for this feature
• Remove custom DataSource, middleware, and workarounds
• Use native Umbraco UI components
• Simpler maintenance long-term

Notes

• The native picker uses uui-combobox-list with uui-combobox-list-option elements
• Need to investigate whether this can be used as a standalone property editor or needs wrapping
• This is a multi-site change (UmBootstrap → downstream projects)

[deanleigh]

Additional context

The native Umbraco "Allowed block types" picker (screenshot from backoffice) shows the kind of UI we want — a combobox listing blocks grouped by type. The difference is:

• Native picker: selects block types from the DataType configuration
• What we need: selects block instances from the current page's block grid, showing their titles

Wider opportunity

This could become a reusable block picker property editor beyond just In Page Navigation. Options:

1. Custom property editor in UmBootstrap — simplest, solves our immediate need
2. Standalone Umbraco package — released on NuGet for the community
3. PR to Umbraco core — contribute directly if there's appetite for it

Other devs have suggested "just build your own property editor" rather than relying on Contentment for this use case.