Add toast notifications

app/components/toast.gjs

@@ -0,0 +1,14 @@
+import Component from '@glimmer/component';
+import { service } from '@ember/service';
+
+export default class ToastComponent extends Component {
+  @service toast;
+
+  <template>
+    {{#if this.toast.isVisible}}
+      <div class="toast-notification">
+        {{this.toast.message}}
+      </div>
+    {{/if}}
+  </template>
+}