Add host moderation controls for rooms

Hosts need practical controls to keep rooms moving and manageable.

Feedback source:
- Kicking users from rooms should be added.
- As host I wish to be able to kick/skip people whenever they are taking too long.
- Limit the amount of people who can join.

Acceptance ideas:
- Host can kick a user from a room.
- Host can force-skip or mark a user as skipping.
- Host can configure a max participant count.
- Kicked/skipped users receive a clear client message.
- Consider separate behavior for spectators vs competitors.