chore(nav): move Clients up to Overview (after Dashboard)

Clients is the most-used screen, so it moves from the 'Clients & billing' group to the
top Overview group, right after Dashboard. Documents/Renewals/SMS credits stay in
Clients & billing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/hq-web/src/nav.ts

@@ -22,6 +22,7 @@ export const NAV_GROUPS: NavGroup[] = [
     items: [
       { to: '/', label: 'Home', icon: LayoutGrid },
       { to: '/dashboard', label: 'Dashboard', icon: LayoutDashboard },
+      { to: '/clients', label: 'Clients', icon: Users },
     ],
   },
   {
@@ -36,7 +37,6 @@ export const NAV_GROUPS: NavGroup[] = [
   {
     label: 'Clients & billing',
     items: [
-      { to: '/clients', label: 'Clients', icon: Users },
       { to: '/documents', label: 'Documents', icon: Files, end: true },
       { to: '/renewals', label: 'Renewals', icon: CalendarClock },
       { to: '/sms-balances', label: 'SMS credits', icon: MessageSquare },