Use `application-side` instead of `client-side`

### Describe the feature

client-side is misleading, as in practice for universally rendered apps the "client" code is executed both on the server and on the client.

We recently introduced this change + a glossary for nuxt-auth, having it here would be beneficial for:
- clarity,
- consistency

https://github.com/sidebase/nuxt-auth

### Additional information

_No response_