feat: gt rig add creates agent beads (gt-h3hak, gt-pinkq)

Bootstrap now creates agent beads for ZFC compliance:
- Always: <prefix>-witness-<rig>, <prefix>-refinery-<rig>
- First rig only: <prefix>-deacon, <prefix>-mayor

Agent beads are created in the rig's beads database (not town beads)
because the daemon looks up beads by prefix routing.

Changes:
- internal/rig/manager.go: Added initAgentBeads() function
- internal/cmd/install.go: Added comment explaining why beads aren't
  created here (no rig exists yet at install time)

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

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

internal/cmd/install.go

@@ -174,6 +174,11 @@ func runInstall(cmd *cobra.Command, args []string) error {
 		} else {
 			fmt.Printf("   ✓ Initialized .beads/ (town-level beads with gm- prefix)\n")
 		}
+
+		// NOTE: Agent beads (gt-deacon, gt-mayor) are created by gt rig add,
+		// not here. This is because the daemon looks up beads by prefix routing,
+		// and no rig exists yet at install time. The first rig added will get
+		// these global agent beads in its beads database.
 	}
 
 	// Initialize git if requested (--git or --github implies --git)
@@ -246,3 +251,4 @@ func initTownBeads(townPath string) error {
 	return nil
 }
 
+