Feat: Pause / skip next run (scheduler)

Idea: For interval (and optionally time-based) schedules, add “Skip next run” so the next due time is ignored once, then the schedule continues. 

In addition: “Pause until [date/time]” or "Pause for X hours/minutes" so the schedule is effectively off until that moment, then auto-resumes. 

Implement by extending the schedule payload and having get_due_schedules / next-run logic respect them. 
