refactor(cli): rename generated modules file and update gitignore pattern

- rename `modules.generated.js` to `modules.client.js` and add `'use client'` directive
- update gitignore to ignore entire `app/.zen/` directory instead of single file
- update layout import to reference new `modules.client.js` filename

templates/app/.zen/modules.client.js

@@ -0,0 +1,4 @@
+// AUTO-GÉNÉRÉ par `npx zen-modules sync` — ne pas modifier à la main.
+'use client';
+
+export {};