feat(roles): switch daemon to config-based roles, remove role beads (Phase 2+3)

Phase 2: Daemon now uses config.LoadRoleDefinition() instead of role beads
- lifecycle.go: getRoleConfigForIdentity() reads from TOML configs
- Layered override resolution: builtin → town → rig

Phase 3: Remove role bead creation and references
- Remove RoleBead field from AgentFields struct
- gt install no longer creates role beads
- Remove 'role' from custom types list
- Delete migrate_agents.go (no longer needed)
- Deprecate beads_role.go (kept for reading existing beads)
- Rewrite role_beads_check.go to validate TOML configs

Existing role beads are orphaned but harmless.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/rig/manager.go

@@ -750,14 +750,12 @@ func (m *Manager) initAgentBeads(rigPath, rigName, prefix string) error {
 			continue // Already exists
 		}
 
-		// RoleBead points to the shared role definition bead for this agent type.
-		// Role beads are in town beads with hq- prefix (e.g., hq-witness-role).
+		// Note: RoleBead field removed - role definitions are now config-based
 		fields := &beads.AgentFields{
 			RoleType:   agent.roleType,
 			Rig:        agent.rig,
 			AgentState: "idle",
 			HookBead:   "",
-			RoleBead:   beads.RoleBeadIDTown(agent.roleType),
 		}
 
 		if _, err := bd.CreateAgentBead(agent.id, agent.desc, fields); err != nil {