+layout.js or +layout.svelte for mixpanel integration in SvelteKit project when +layout.server.js already exists

I want to integrate Mixpanel to my SvelteKit project by following official documentation at https://developer.mixpanel.com/docs/javascript-quickstart

To integrate I have initilise mixpanel using code

import mixpanel from 'mixpanel-browser';

mixpanel.init('YOUR_TOKEN', {debug: true}); 
mixpanel.track('test event');

Where should I add this mixpanel initialisation so I can track events on my desired pages?

My project already have +layout.server.js and I can not initilise mixpanel in this file becase this will run on server side.

Now I have choice of +layout.js and +layout.svelte.
If I choose to use +layout.js then it will conflict with +layout.server.js
If I choose to use +layout.svelte then I am not sure if I can expose mixpanel globally to child pages.

So what should be right way to integrate mixpanel if +layout.server.js is present in project?