feat(message-gateway): add admin channel cards and per-type forms

frontend/components/layout/sidebar.tsx

@@ -56,6 +56,7 @@ import {
   Home,
   Layers,
   LogOut,
+  MessagesSquare,
   Settings,
   ShieldCheck,
   Terminal,
@@ -84,6 +85,7 @@ const adminItems: NavItem[] = [
   { titleKey: 'storage', url: '/admin/files', icon: FolderOpen },
   { titleKey: 'database', url: '/admin/database', icon: Database },
   { titleKey: 'push', url: '/admin/push', icon: Bell },
+  { titleKey: 'messageGateway', url: '/admin/message-gateway', icon: MessagesSquare },
   { titleKey: 'logs', url: '/admin/logs', icon: Terminal },
   { titleKey: 'system', url: '/admin/system', icon: ShieldCheck },
   { titleKey: 'adminSettings', url: '/admin/settings', icon: Settings },