Add slot management commands:
- bd slot set <agent> <slot> <bead> - set slot (error if occupied)
- bd slot clear <agent> <slot> - clear slot
- bd slot show <agent> - show all slots
These enforce cardinality constraints for agent bead slots.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>