refactor: hide Models nav entry from sidebar

89cat locks token server to api2.is89.com — users should not add
arbitrary AI providers through the Models page.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/components/layout/Sidebar.tsx

@@ -20,7 +20,6 @@ import {
   Pencil,
   Check,
   X,
-  Cpu,
   ImagePlus,
   Moon,
   ChevronRight,
@@ -313,7 +312,6 @@ export function Sidebar() {
   const coreNavItems = [
     { to: '/', icon: <LayoutDashboard className="h-4 w-4" strokeWidth={2} />, label: t('sidebar.dashboard'), testId: 'sidebar-nav-dashboard' },
     { to: '/chat', icon: <MessageSquare className="h-4 w-4" strokeWidth={2} />, label: t('sidebar.chat'), testId: 'sidebar-nav-chat' },
-    { to: '/models', icon: <Cpu className="h-4 w-4" strokeWidth={2} />, label: t('sidebar.models'), testId: 'sidebar-nav-models' },
     { to: '/agents', icon: <Bot className="h-4 w-4" strokeWidth={2} />, label: t('sidebar.agents'), testId: 'sidebar-nav-agents' },
     { to: '/channels', icon: <Network className="h-4 w-4" strokeWidth={2} />, label: t('sidebar.channels'), testId: 'sidebar-nav-channels' },
     { to: '/skills', icon: <Puzzle className="h-4 w-4" strokeWidth={2} />, label: t('sidebar.skills'), testId: 'sidebar-nav-skills' },