Delete account and all data

Sad to see you go... but it makes sense to add a button in the settings to delete an account.

This can be split in two tasks:

[x] Create the button (with confirmation modal) in the settings
[x] Implement the actual code deleting the user (& everything else should cascade automatically in the DB)

I think it's easier if I work on the second part with access to the supabase panel but if someone wants to work on the UI first, you're welcome!

Balastrong / myntenance