- Add sessions table to database with projectId and deletedAt columns
- Create POST /api/sessions/:id/move endpoint to reassign sessions
- Update DELETE /api/projects/:id to cascade soft-delete to sessions
- Support moving sessions between projects or to unassigned state
- Handle both active (in-memory) and historical sessions
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>