feat: add multi-tenant client management for admins

- Add tenants API endpoints (list, get, create)
- Add tenant middleware override via X-View-Tenant header
- Add TenantSelector dropdown component in header
- Add tenant view store with persistence
- Add Clientes management page
- Update all navigation layouts with Clientes link for admins

Admins can now:
- View list of all clients
- Create new clients with automatic schema setup
- Switch between viewing different clients' data
- See which client they are currently viewing

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/components/layouts/topnav.tsx

@@ -14,6 +14,7 @@ import {
   Bell,
   Users,
   ChevronDown,
+  Building2,
 } from 'lucide-react';
 import { useAuthStore } from '@/stores/auth-store';
 import { logout } from '@/lib/api/auth';
@@ -31,12 +32,20 @@ const navigation = [
   { name: 'Config', href: '/configuracion', icon: Settings },
 ];
 
+const adminNavigation = [
+  { name: 'Clientes', href: '/clientes', icon: Building2 },
+];
+
 export function TopNav() {
   const pathname = usePathname();
   const router = useRouter();
   const { user, logout: clearAuth } = useAuthStore();
   const [userMenuOpen, setUserMenuOpen] = useState(false);
 
+  const allNavigation = user?.role === 'admin'
+    ? [...navigation.slice(0, -1), ...adminNavigation, navigation[navigation.length - 1]]
+    : navigation;
+
   const handleLogout = async () => {
     try {
       await logout();
@@ -61,7 +70,7 @@ export function TopNav() {
 
         {/* Navigation */}
         <nav className="flex-1 flex items-center gap-1">
-          {navigation.map((item) => {
+          {allNavigation.map((item) => {
             const isActive = pathname === item.href || pathname.startsWith(`${item.href}/`);
             return (
               <Link