Add comprehensive async collaboration system for PRD/Epic development:
PRD & Epic Crowdsourcing:
- Create, open feedback rounds, synthesize, and sign-off workflows
- LLM-powered synthesis engine for conflict resolution
- Configurable sign-off thresholds (count, percentage, required approvers)
- Unified "my-tasks" view across PRDs and Epics
Story Coordination:
- Story locking/checkout for preventing concurrent work
- Lock status and unlock workflows
- Available stories view with lock status
Multi-Channel Notifications:
- GitHub @mentions, Slack webhooks, Email (SMTP/SendGrid/SES)
- Event-driven notifications for feedback/signoff requests
- Priority-based retry logic for urgent notifications
Cache System Extensions:
- PRD and Epic document caching with metadata migration
- Staleness detection and atomic file operations
- User task queries and extended statistics
GitHub integration is optional (disabled by default) - existing local-only
projects continue to work unchanged.
Includes 673 passing tests with comprehensive coverage for all new modules.
Note: Library files use CommonJS for Node.js compatibility. ESLint rules
for ES modules may need configuration adjustment.