feat(cli): integrate zen-modules sync into project initialization

- add postinstall, dev, and build scripts to run `zen-modules sync`
- append `app/.zen/modules.generated.js` to .gitignore during init
- add generated modules file template with empty modules export
- import modules.generated.js in app layout and pass modules to initializeZen

templates/app/.zen/modules.generated.js

@@ -0,0 +1,3 @@
+// AUTO-GÉNÉRÉ par `npx zen-modules sync` — ne pas modifier à la main.
+
+export const modules = [];

templates/app/layout.js

@@ -1,4 +1,5 @@
 import "@styles/globals.css";
+import './.zen/modules.generated.js';
 import { ZenProvider } from '@zen/core/features/provider';
 import { THEME_INIT_SCRIPT } from '@zen/core/themes';