Uniform navigation and mega menus

Navigation in Uniform is a chain of small components, authored and reordered in the visual editor. The hard part is that a slot hands a parent already-rendered, opaque children — so a menu shell that needs its children's labels, to draw a category rail or a mobile section heading, cannot get them by reading the slot. Everything here follows from that.

Workflow

1. Discover before you model

Never assume the project is greenfield, and never assume which component library it uses. Find out which of these you are in — the answer changes every later step. See references/discovery.md for the greps.