Summary

Implement the EventDrivenStrategy for the pluggable ceremony scheduling system.

Ceremonies subscribe to engine events with configurable debounce. No fixed schedule -- ceremonies fire reactively based on event subscriptions.

Design Reference

See Ceremony Scheduling design page -- "Event-Driven" strategy section.

Key Behaviors

• should_fire_ceremony: checks if the configured event has fired and debounce threshold is met (e.g., fire standup once per 5 task_completed events)
• should_transition_sprint: returns target status on configured event (e.g., sprint_backlog_empty triggers IN_REVIEW)
• on_sprint_activated: subscribes to relevant engine events via lifecycle hooks
• on_sprint_deactivated: unsubscribes from events
• on_task_completed, on_task_blocked, etc.: count events for debounce tracking
• Default velocity calculator: PointsPerSprintVelocityCalculator

Implementation

• New: src/synthorg/engine/workflow/strategies/event_driven.py
• New: tests/unit/engine/workflow/strategies/test_event_driven.py
• Implement CeremonySchedulingStrategy protocol from feat: sprint ceremony runtime scheduler with task-driven cadence support #961

Also implement: PointsPerSprintVelocityCalculator

• New: src/synthorg/engine/workflow/velocity_calculators/points_per_sprint.py
• New: tests/unit/engine/workflow/velocity_calculators/test_points_per_sprint.py
• Simplest calculator: pts/sprint with no time or task normalization

Dependencies

• feat: sprint ceremony runtime scheduler with task-driven cadence support #961 (protocol interfaces + reference implementation)