Fix chi routing to CardDAV handler

We could probably just stick to net/http here...

cmd/tokidoki/main.go

@@ -34,7 +34,7 @@ func main() {
 	mux.Use(authProvider.Middleware())
 
 	backend := storage.NewPostgreSQL()
-	mux.Handle("/", &carddav.Handler{Backend: backend})
+	mux.Mount("/", &carddav.Handler{Backend: backend})
 
 	server := http.Server{
 		Addr:    addr,