Match page width to sso-manager-node; gate Audit nav to admins

- Dashboard, Sessions, and Audit pages now wrap their content in
  <div class="container mt-4">, matching sso-manager-node/proxy's width
  instead of rendering full-bleed inside the fluid shell.
- Audit's nav entry now carries groups: ['admin'] (utils/ui.js), reusing
  the existing synthetic-admin-group nav-gating convention -- the API
  route was already server-side admin-gated, this closes the last gap by
  hiding the nav link/page for non-admins too.
- app-base.js (byte-identical across the 3 apps): added
  app.util.revealItem() and the --sw-content-offset sticky-positioning
  variable, carried over from the same round of changes in
  sso-manager-node/proxy. Not yet called anywhere in this app -- no
  sticky/reveal use case here yet -- but keeps the shared file in sync.

nodejs/utils/ui.js

@@ -37,6 +37,6 @@ module.exports = {
 	nav: [
 		{href: '/dashboard', icon: 'fa-solid fa-gauge-high', label: 'Dashboard', groups: []},
 		{href: '/sessions', icon: 'fa-solid fa-plug-circle-bolt', label: 'Sessions', groups: []},
-		{href: '/audit', icon: 'fa-solid fa-clipboard-list', label: 'Audit', groups: []},
+		{href: '/audit', icon: 'fa-solid fa-clipboard-list', label: 'Audit', groups: ['admin']},
 	],
 };