Invite commands

Fieldbot compares invite usage before and after a member joins. When it cannot make a reliable match, it stores the result as unknown instead of guessing.

Command	Purpose
/invites [user]	Shows active, suspicious, left, and manual invite counts.
/invite-leaderboard	Opens the paginated server invite leaderboard.
/invite-add user amount [reason]	Adds a positive or negative manual correction. Requires Manage Server.
/invite-channel set|reset|status	Manages invite tracking state and the log channel.

Total invite score is based on active invites plus manual corrections. Suspicious and left members do not increase the total.