fix(stockholm): match setupRouter signature in router_test

setupRouter gained a *stockholm.Handler parameter on this branch, but
the test left over from the previous signature still called it with
one argument, breaking `go vet ./...`. Pass nil — Stockholm is opt-in
and not exercised in this test.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cmd/soundtouch-service/router_test.go

@@ -128,7 +128,7 @@ func TestPUTRenameRoutesToLocalHandler(t *testing.T) {
 	_ = ds.Initialize()
 
 	server := handlers.NewServer(ds, nil, "http://localhost:8000", false, false, false)
-	r := setupRouter(server)
+	r := setupRouter(server, nil)
 	ts := httptest.NewServer(r)
 	defer ts.Close()