feat(ui): E31 S4b — the admin pages behind one rail row, Configuration as a sectioned list, Statistics as tiles and bars

- NavRailGroup: one "Admin" rail row opening a panel of the admin pages (links, so a
  middle-click still opens a tab); the rail fits 133% zoom without a hidden scroll
- sysconfig.SECTIONS orders the config groups under four headings (every group in exactly
  one, test-held); the page shows them as Settings' side list (Tabs `group` headings);
  the lone registration group reads "Registration" under "Access"
- StatTiles / StatTile / StatBars: the Statistics overview's figures as tiles, the
  per-operation quota use as horizontal bars (a zero draws none)

frontend/src/components/ui/pressableSelectable.contract.test.ts

@@ -46,7 +46,10 @@ const PLAIN: Record<string, [number, string]> = {
   "ui/ActionMenu.tsx": [1, "a menu row"],
   "ui/BackToTop.tsx": [1, "a control"],
   "ui/CommandPalette.tsx": [1, "a command row"],
-  "ui/NavRail.tsx": [1, "the action rows (About, Sign out); a page row is a link (E31)"],
+  "ui/NavRail.tsx": [
+    2,
+    "the action rows (About, Sign out) and the group row that opens its panel; a page row is a link (E31)",
+  ],
   "ui/PanelGroup.tsx": [2, "a group's collapse toggle and its label"],
   "ui/SidePanel.tsx": [2, "panel controls"],
   "ui/tableHeader.tsx": [1, "a column's sort header"],