if we want some HMR magic for it is related to hot reload - if you want the store to reload only a single module on changes during development instead of trigger rebuild.
And yes, you can organize the store however you want - put everything in index.js, or on the same level… it’s up to you. Quasar scaffolds very granular setup at start, but you can definitely reorganize it for your needs. I tend to have just per-file modules, because they are usually pretty small in my projects. In the end store is just a bunch of JS objects and functions that you put inside the Store constructor. There is no restriction on how you organize them.
You can reset the store with some mutation nulling all variables like Max said. I often use dynamic modules and just register one on login and unregister it on logout. That way I can just throw out all the data easily.