Users can define a custom order of templates (e.g., Push → Pull → Legs).
Based on the last completed session, the next workout in rotation is
recommended via a prominent banner and the floating action button.
- New WorkoutSchedule MongoDB model (per-user template order)
- GET/PUT /api/fitness/schedule API endpoints
- Schedule editor modal with reorder and add/remove
- Action button starts next scheduled workout when schedule exists
