feat: Standardize agent bead naming to prefix-rig-role-name (gt-zvte2)

Implements canonical naming convention for agent bead IDs:
- Town-level: gt-mayor, gt-deacon (unchanged)
- Rig-level: gt-<rig>-witness, gt-<rig>-refinery (was gt-witness-<rig>)
- Named: gt-<rig>-crew-<name>, gt-<rig>-polecat-<name> (was gt-crew-<rig>-<name>)

Changes:
- Added AgentBeadID helper functions to internal/beads/beads.go
- Updated all ID generation call sites to use helpers
- Fixed session parsing in theme.go, statusline.go, agents.go
- Updated doctor check and fix to use canonical format
- Updated tests for new format

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/cmd/prime.go

@@ -1137,31 +1137,32 @@ 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
 // Returns empty string for unknown roles.
 func getAgentBeadID(ctx RoleContext) string {
 	switch ctx.Role {
 	case RoleMayor:
-		return "gt-mayor"
+		return beads.MayorBeadID()
 	case RoleDeacon:
-		return "gt-deacon"
+		return beads.DeaconBeadID()
 	case RoleWitness:
 		if ctx.Rig != "" {
-			return fmt.Sprintf("gt-witness-%s", ctx.Rig)
+			return beads.WitnessBeadID(ctx.Rig)
 		}
 		return ""
 	case RoleRefinery:
 		if ctx.Rig != "" {
-			return fmt.Sprintf("gt-refinery-%s", ctx.Rig)
+			return beads.RefineryBeadID(ctx.Rig)
 		}
 		return ""
 	case RolePolecat:
 		if ctx.Rig != "" && ctx.Polecat != "" {
-			return fmt.Sprintf("gt-polecat-%s-%s", ctx.Rig, ctx.Polecat)
+			return beads.PolecatBeadID(ctx.Rig, ctx.Polecat)
 		}
 		return ""
 	case RoleCrew:
 		if ctx.Rig != "" && ctx.Polecat != "" {
-			return fmt.Sprintf("gt-crew-%s-%s", ctx.Rig, ctx.Polecat)
+			return beads.CrewBeadID(ctx.Rig, ctx.Polecat)
 		}
 		return ""
 	default: