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/beads/beads.go

@@ -44,8 +44,8 @@ type Issue struct {
 
 	// Agent bead slots (type=agent only)
 	HookBead   string `json:"hook_bead,omitempty"`   // Current work attached to agent's hook
-	RoleBead   string `json:"role_bead,omitempty"`   // Role definition bead (shared)
 	AgentState string `json:"agent_state,omitempty"` // Agent lifecycle state (spawning, working, done, stuck)
+	// Note: role_bead field removed - role definitions are now config-based
 
 	// Counts from list output
 	DependencyCount int `json:"dependency_count,omitempty"`