Add a note if user attempts to register with (apparently) an email

src/components/RegisterPage.vue

@@ -52,6 +52,8 @@ export default {
     methods: {
         register() {
             if (!this.username || !this.password) return;
+            if (this.username.includes("@") && !confirm(this.$t("info.register_no_email_note"))) return;
+
             this.fetchJson(this.authApiUrl() + "/register", null, {
                 method: "POST",
                 body: JSON.stringify({