Self-contained nav — staging preview

This page renders the new Imagen Navigation SC module. The top-level items (Why Reuters Imagen, Platform, Resources, Partners) and everything inside their mega panels are stored in a single Nav Items field on the module — no HubSpot menu, no "For Mega Menu" placeholders, and no positional index mapping.

Hover or keyboard-focus a top-level item to open its mega panel. It should look and behave identically to the live header.

Staging only — the live global header is untouched.