You can in fact import mirage utilities and create your custom server in the components but that is very cumbersome, this is what's in their documentation and their examples are very poorly made unfortunately...
In your case you have already defined your server, so why would you import the entire file multiple times into different part of your application?
You also don't do modular import hence tree shaking will not happen which will bloat up your application.
Mirage.js will monitor and intercept your HTTP requests and perform the defined actions if you hit a valid path predefined by you. If you have 1 page where you have indeed imported the server then you navigate to another page where you did not I do not believe you should have the mirage code running anymore hence no more mock api for you
You only need to import the server at your root/entry point if that did not work for you then there is a problem somewhere else, perhaps you did not remove the other server imports from your other files and you have some clashes in your app because of that.