DashboardLayoutSection was a 620-line component. Its parts move to
components/settings/dashboard-layout/:
- layout-model: the reorder and hero-kind helpers and the label maps
- use-dashboard-layout-draft: the tokened read, the draft, save and
reset (with the snapshot and digest refresh) and the draft edits
- hero-settings-fieldset: the top card's switch, lead and highlights
- widget-lists: the sortable web list, the native-only group and rows
The section composes them. Markup and behaviour are unchanged.
