feat: add the admin layout shell

assets/controllers/mobilenav_controller.js

@@ -0,0 +1,22 @@
+import { Controller } from '@hotwired/stimulus';
+
+/*
+ * Off-canvas mobile navigation drawer. Ported from myep.
+ *
+ * Two instances cooperate through a Stimulus outlet: the opener button in the header and the
+ * drawer itself. Purely client-side -- htmx is not involved.
+ */
+export default class extends Controller {
+    static outlets = ['mobilenav'];
+    static classes = ['closed'];
+
+    trigger({ params: { mode } }) {
+        this.mobilenavOutlet.toggle(mode);
+    }
+
+    toggle(mode) {
+        // Added only now, so the drawer does not animate into place on first paint.
+        this.element.classList.add('transition-transform', 'duration-300');
+        this.element.classList.toggle(this.closedClass, 'close' === mode);
+    }
+}