Replace hotwire with htmx

In the process, also improve the feedback from the import/add feed
forms.

I also replaced the frontend code to replace utc timestamps with local
time strings with @hotwired/stimulus with vanilla js.

frontend/js/index.ts

@@ -1,9 +1,4 @@
-import { Application } from "@hotwired/stimulus";
-
-import LocalTimeController from "./local_time_controller";
-
 // import CSS so it gets named with a content hash that busts caches
 import "../css/styles.css";
 
-window.Stimulus = Application.start();
-window.Stimulus.register("local-time", LocalTimeController);
+import "./localTimeController";