refactor: remove unused isFirstRig param from initAgentBeads (gt-fugmy)

The isFirstRig parameter was no longer used - it was being assigned
to a blank identifier. Since initAgentBeads is an internal function
with only 2 callers in this repo, remove the parameter entirely.

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

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

internal/rig/manager_test.go

@@ -381,7 +381,7 @@ esac
 	t.Setenv("BEADS_DIR", "") // Clear any existing BEADS_DIR
 
 	manager := &Manager{townRoot: townRoot}
-	if err := manager.initAgentBeads(rigPath, "demo", "gt", false); err != nil {
+	if err := manager.initAgentBeads(rigPath, "demo", "gt"); err != nil {
 		t.Fatalf("initAgentBeads: %v", err)
 	}