Add an optional `onApproval` callback to OrchestratorConfig that gates
between task execution rounds. After each batch of parallel tasks
completes, the callback receives the completed tasks and the tasks about
to start, returning true to continue or false to abort gracefully.
Key changes:
- Add 'skipped' to TaskStatus for user-initiated abort (distinct from 'failed')
- Add skip(), skipRemaining(), cascadeSkip() to TaskQueue
- Add 'task_skipped' to OrchestratorEvent for progress monitoring
- Approval gate in executeQueue() with try/catch for callback errors
- Synthesis prompt now includes skipped tasks section
- 17 new tests covering queue skip operations and orchestrator integration
Closes#32
JackChen