[REFACTOR]: templates in gjs

### What to refactor

Make templates (`ember/app/templates/*`) gjs using [ember-route-template](https://github.com/discourse/ember-route-template)### 

### Why refactor it

more gjs

### How to refactor it

`pnpm ember i ember-route-template`
then edit things

### Required

- [X] I have checked past issues to ensure that this isn't a duplicate.