feat: add htmx server-side plumbing

assets/controllers/modal_controller.js

@@ -0,0 +1,14 @@
+import { Controller } from '@hotwired/stimulus';
+
+/*
+ * Closes an htmx-loaded modal by removing it from the DOM.
+ *
+ * Wired to the backdrop, the X button and a `modal-close` window event, so a fragment swapped
+ * into the modal can dismiss it with `htmx.trigger(window, 'modal-close')` or an HX-Trigger
+ * header. Opening is htmx's job; closing never needs a round trip.
+ */
+export default class extends Controller {
+    close() {
+        this.element.remove();
+    }
+}