Enhance the reliability and observability of the task execution engine
by introducing retry mechanisms, idempotency, and structured progress
tracking.
- Implement centralized retry logic with exponential backoff support
in `JobLifecycle`.
- Add `retry_task` API endpoint and `TaskManager` method for manual
task restarts.
- Introduce task idempotency using `_idempotency_key` to prevent
duplicate executions.
- Add `retry_count`, `max_retries`, `last_error`, and `progress` fields
to the `Task` model and ensure persistence via `TaskPersistenceService`.
- Upgrade `SchedulerService` to use differential synchronization with
the persistent `SQLAlchemyJobStore` for better job durability.
- Implement structured heartbeat logging to support real-time progress
updates.
- Update project documentation and ADRs to reflect the new plugin
runtime and task resilience patterns.
- Add comprehensive unit and integration tests for the new task
lifecycle features.
