feat(design): the NavRail primitive with optional short labels, the flat surfaces onto roles (E28 S3d3, B7/B5)

frontend/src/components/ui/README.md

@@ -42,7 +42,7 @@ domain-free.
 | actions & inputs     | `Button`, `IconButton`, `Pressable`, `Chip` + `chipStyles`, `DragHandle` (one per button family, docs/DESIGN.md; a raw `<button>` outside this folder is a lint error), `Input` + `fieldStyles`, `NativeControls`, `SelectTrigger` (the field family; a raw `<input>` is a lint error), `useReturnFocus`, `surfaces` (the                                                                                            |
 
 B5 glass roles; a bare glass class is a lint error), `Badge` (a static label), `LinkButton` / `IconLink` (a
-link wearing the button face) over `buttonStyles`, `form`, `DraftSaveBar`, `Combobox`, `FilterSelect`, `SegmentedToggle`, `SortControl`, `ColumnSortControl`, `PriorityStepper`, `UndoToolbar` |
+link wearing the button face) over `buttonStyles`, `Skeleton` (B8 first loads, through `LoadingState shape`), `NavRail` (B7), `form`, `DraftSaveBar`, `Combobox`, `FilterSelect`, `SegmentedToggle`, `SortControl`, `ColumnSortControl`, `PriorityStepper`, `UndoToolbar` |
 | data display | `DataTable`, `tableHeader` + `tableAlign`, `Pager` + `pagerContent`, `VirtualGrid` + `gridColumns` (the column/width maths, incl. the ultrawide `maxCols` cap), `readAhead`, `Carousel`, `NavGrid` (a plain grid, list or table body the keyboard walks — `DataTable`, `VirtualGrid` and `Carousel` take `keyboardNav`), `Avatar`, `CountBadge`, `ItemCount`, `FilterChipGroup` |
 | page & panel structure | `PageShell` + `pageToolbarSlot`, `PageScroller`, `PanelGroup`, `PanelGroups`, `Tabs`, `BackToTop` |
 | state & messaging | `QueryState`, `Banner`, `InlineNotice` |