Prevent accidental scramble advancement before competitors are resolved

Rooms should not accidentally generate a new scramble while competing users still need to submit, skip, or be explicitly ignored.

Feedback source:
- Stop rooms from accidentally generating a new scramble when not all competing users have submitted a result.
- Grey out scramble and timer, not just timer.

Acceptance ideas:
- Confirm the server-side condition for advancing scrambles.
- Require every active competitor to have a result, be skipping, be forced-skipped, or no longer be active.
- Make the client UI clearly indicate when the current scramble is no longer available for timing.