エラー Vue/Vuetify - Unknown custom element: <v-app> - did you register the component correctly?

NG

new Vue({
    el: "#app",
    components: { App },
    template: "<App/>"
});

Vue.use(Vuetify);

OK
new Vue()の前にVue.use(Vuetify)しないとダメらしい

Vue.use(Vuetify);

new Vue({
    el: "#app",
    components: { App },
    template: "<App/>"
});

pluginsフォルダを読み込む場合
こんな感じで冗長になる
main.js

import Vue from 'vue'
import App from './App.vue'
import router from './router'
import store from './store'
import Vuetify from 'vuetify'
import 'vuetify/dist/vuetify.min.css'
import VueSession from 'vue-session'

import vuetify from './plugins/vuetify'
// import Vuetify from "vuetify/lib"
Vue.use(Vuetify)
Vue.use(VueSession)

Vue.config.productionTip = false

/* eslint-disable no-new */
new Vue({
  router,
  store,
  vuetify,
  render: h => h(App)
}).$mount('#app')