AdaptiveTwoPane

A two-slot adaptive layout: first and second are stacked in a single column on compact/medium windows and shown side-by-side once the window is large enough to warrant a second pane.

The split decision is delegated to calculatePaneScaffoldDirective rather than a hardcoded width breakpoint. The directive only grants a second horizontal partition at the expanded width class (>= 840dp) by default — matching the Material adaptive guidance that side-by-side panes are an expanded-width pattern, not a medium (600dp) one — and it is hinge / multi-window aware. This is the same primitive the app's navigation-based scaffolds (MeshtasticNavDisplay) use, so both surfaces flip to two panes at the same breakpoint.

When split, the panes are hosted in a SupportingPaneScaffold so the divider is a draggable VerticalDragHandle, giving parity with the list-detail / supporting-pane scenes elsewhere in the app. Both slots keep their ColumnScope receiver, so callers are unchanged.