Phase 7 Task 4: Add collaboration API endpoints and schema
- Add collaboration_manager import and COLLABORATION_AVAILABLE flag
- Add get_collab_manager() singleton function
- Add collaboration API endpoints:
- Project share links (create, list, verify, access, revoke)
- Comments (add, get, update, resolve, delete)
- Change history (get, stats, versions, revert)
- Team members (invite, list, update role, remove, check permissions)
- Add collaboration tables to schema.sql:
- project_shares, comments, change_history, team_members
- Related indexes for performance