crew_add.go: Use gt-crew-role instead of per-instance role bead
polecat/manager.go: Add RoleBead field pointing to gt-polecat-role
Per agent-as-bead design, role beads are shared class definitions.
Each agent bead references its role via the role_bead field/slot.
Fixes gt-ne9he
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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