fix(theme): stabilize tenant switch theme propagation and toggle race handling

Task: REVIEW-USER-THEME-001

pages/admin/users/switch-tenant().php

@@ -89,6 +89,7 @@ if (Request::wantsJson()) {
         'ok' => true,
         'tenant_id' => $tenantId,
         'tenant' => $result['tenant'] ?? null,
+        'theme' => currentTheme(),
     ]);
     return;
 }