Some way to limit user team switching

[Artemis21]

Heavy ratelimit? Though this should not apply to users changing it with the manage_account_teams permission.

[Artemis21]

Perhaps:

• only allow people to set their own team if they don't already have one
• display a confirmation dialogue when trying to set team, to avoid misclicks
• if they do set the wrong one someone with manage_account_teams must change it