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/api/src/routes/tenants.routes.ts

@@ -0,0 +1,13 @@
+import { Router } from 'express';
+import { authenticate } from '../middlewares/auth.middleware.js';
+import * as tenantsController from '../controllers/tenants.controller.js';
+
+const router = Router();
+
+router.use(authenticate);
+
+router.get('/', tenantsController.getAllTenants);
+router.get('/:id', tenantsController.getTenant);
+router.post('/', tenantsController.createTenant);
+
+export { router as tenantsRoutes };