- Add computePreconditions and computeBlockedByFailure functions to node-status.ts
- Add registerStartEffect and registerAbortEffect for automatic state transitions
- Start effect: idle/waiting -> ready when preconditions met
- Abort effect: idle/waiting -> aborted when blockedByFailure true
- Refactor WorkflowReactiveRoot to use node-status.ts functions
- Root nodes auto-transition from idle to ready (no predecessors = preconditions true)
- Add AbortEffectOptions with abortDependents policy support
- Add comprehensive unit tests for all precondition and failure isolation scenarios
