Manage slot permission

[bcm]

Define a specialized permission for managing slots (create, view, update, delete).

Benefit: Enables delegation of schedule management to support GM-driven scheduling approaches.

https://warhorn.groovehq.com/tickets/447
https://warhorn.groovehq.com/tickets/586

[bcm]

Implemented with a new "manage schedule" permission that enables management of both slots and sessions.