Also bundle css with bun so it busts caches

And updates the `build.rs` script so that it also builds a manifest.txt
for css files.

frontend/js/index.ts

@@ -0,0 +1,9 @@
+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);