"Show X now" now persists indefinitely (survives restarts too, it's in
config.json) instead of auto-expiring back to rotation after 5 minutes.
Implemented by reusing the existing rotation.enabled flag rather than a
separate scheduler-side timer: pinning a screen sets rotation.enabled=False
and records which screen in a new pinned_screen config field. Re-enabling
rotation -- either the "Resume automatic" button or just checking
"Enabled" again on the Rotation settings page -- clears the pin and
resumes normal cycling either way.
Navidrome priority is unchanged: still checked first, still preempts a
pin the instant something's playing, same as it already preempted
rotation.
Verified end-to-end: pin persists across many scheduler ticks (previously
would have reverted after 5 min), both resume paths (button and settings
checkbox) clear it correctly.