feat(14-04): add top-level PAX8 nav entry

- New top-level navigationItems entry (href: /pax8, icon: ShoppingCart)
- Not added to the Engagement/Admin visibleItems super-admin gate — visible to all authenticated users on both desktop NavigationMenu and mobile Sheet (D-07)

components/navigation/app-navigation.tsx

@@ -18,6 +18,7 @@ import {
   Search,
   AlertTriangle,
   ChevronDown,
+  ShoppingCart,
 } from 'lucide-react';
 import {
   NavigationMenu,
@@ -60,6 +61,12 @@ const navigationItems: NavItem[] = [
     icon: Server,
     description: 'Manage IT assets and devices'
   },
+  {
+    title: 'PAX8',
+    href: '/pax8',
+    icon: ShoppingCart,
+    description: 'PAX8 companies, subscriptions, and cost breakdown'
+  },
   {
     title: 'Backup Status',
     icon: HardDrive,