refactor(ui): extract adaptive panel rail layout

src/ui/panelRails.js

@@ -0,0 +1,5 @@
+export { layoutLeftPanelRail } from './leftPanelRail.js';
+export { layoutRightPanelRail } from './rightPanelRail.js';
+export { measurePanelNaturalHeight } from './panelMeasurement.js';
+export { resolveHudRailLayout, shouldHideCollapsedRightPanels } from './panelRailGeometry.js';
+export { allocatePanelStackHeights, panelStackAutoCollapseIndices, resolveLeftStackBottomBoundary, resolvePanelStackCorridor } from '../panelStackLayout.js';