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/lib/hooks/use-tenants.ts

@@ -0,0 +1,20 @@
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
+import { getTenants, createTenant, type CreateTenantData } from '@/lib/api/tenants';
+
+export function useTenants() {
+  return useQuery({
+    queryKey: ['tenants'],
+    queryFn: getTenants,
+  });
+}
+
+export function useCreateTenant() {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: (data: CreateTenantData) => createTenant(data),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['tenants'] });
+    },
+  });
+}