Fix agent bead prefix mismatch for rigs with custom prefixes (bd-otyh)

When spawning polecats in rigs with custom prefixes (e.g., beads uses bd-
instead of gt-), agent beads were being created with hardcoded gt- prefix,
causing warnings like issue ID gt-beads-polecat-obsidian does not match
configured prefix bd.

Changes:
- polecat/manager.go: agentBeadID() now looks up the rigs configured prefix
  from routes.jsonl via beads.GetPrefixForRig()
- prime.go: getAgentBeadID() now uses prefix lookup for rig-level agents
  (witness, refinery, polecat, crew)

Town-level agents (mayor, deacon) continue to use gt- prefix as expected.

internal/cmd/prime.go

@@ -1171,8 +1171,17 @@ func getAgentFields(ctx RoleContext, state string) *beads.AgentFields {
 
 // getAgentBeadID returns the agent bead ID for the current role.
 // Uses canonical naming: prefix-rig-role-name
+// The prefix is looked up from routes.jsonl to support rigs with custom prefixes.
 // Returns empty string for unknown roles.
 func getAgentBeadID(ctx RoleContext) string {
+	// Helper to get prefix for rig-level agents
+	getPrefix := func() string {
+		if ctx.TownRoot != "" && ctx.Rig != "" {
+			return beads.GetPrefixForRig(ctx.TownRoot, ctx.Rig)
+		}
+		return "gt" // Default prefix
+	}
+
 	switch ctx.Role {
 	case RoleMayor:
 		return beads.MayorBeadID()
@@ -1180,22 +1189,22 @@ func getAgentBeadID(ctx RoleContext) string {
 		return beads.DeaconBeadID()
 	case RoleWitness:
 		if ctx.Rig != "" {
-			return beads.WitnessBeadID(ctx.Rig)
+			return beads.WitnessBeadIDWithPrefix(getPrefix(), ctx.Rig)
 		}
 		return ""
 	case RoleRefinery:
 		if ctx.Rig != "" {
-			return beads.RefineryBeadID(ctx.Rig)
+			return beads.RefineryBeadIDWithPrefix(getPrefix(), ctx.Rig)
 		}
 		return ""
 	case RolePolecat:
 		if ctx.Rig != "" && ctx.Polecat != "" {
-			return beads.PolecatBeadID(ctx.Rig, ctx.Polecat)
+			return beads.PolecatBeadIDWithPrefix(getPrefix(), ctx.Rig, ctx.Polecat)
 		}
 		return ""
 	case RoleCrew:
 		if ctx.Rig != "" && ctx.Polecat != "" {
-			return beads.CrewBeadID(ctx.Rig, ctx.Polecat)
+			return beads.CrewBeadIDWithPrefix(getPrefix(), ctx.Rig, ctx.Polecat)
 		}
 		return ""
 	default: