Breadcrumbs from the Uniform project map

The project map already stores the page hierarchy, a label for every level, and every level's path template. A breadcrumb component reads that tree, asks the Route API for each ancestor's title, and renders the result.

Project map fundamentals — nodes, dynamic inputs, route matching — are in the uniform-sdk skill (references/routing.md).

The five inputs

Everything below is a pure function of these. Get them once, at the top of the component.