Verification & reaction roles

Verification gates new members behind a button:

!verifysetup @verified_role [#channel] · post the panel and enable it.
!verifyunverified @role · role applied on join until verified.
!verifydisable · !verifystatus.

Reaction roles let members self-assign roles:

!reactionroles create [#channel] · a quick wizard.
!reactionroles list · !reactionroles delete <message id>.