Fixes #0000

When trying to access the frontend route using app.current.get('routeName'), undefined was returned due to the abnormal definition of the frontend route with the custom resolver.

Changes proposed in this pull request:
This PR uses the frontend extender instead and moves the check into the component itself.

Reviewers should focus on:

Screenshot

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).

Required changes:

• Related Flarum core extension PR's: (Omit this section if irrelevant)