Add role_type and rig labels to agent beads for filtering queries.
Changes:
- Add RoleType/Rig to CreateArgs and UpdateArgs in RPC protocol
- Auto-add role_type:<value> and rig:<value> labels when creating/updating agents
- Add --role-type and --agent-rig flags to bd create (requires --type=agent)
- Add bd agent backfill-labels command to update existing agent beads
This enables queries like:
bd list --type=agent --label=role_type:witness
bd list --type=agent --label=rig:gastown
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>