Simplify attachSearchBox and restore the CSS comment

- collapse the render/keydown/select helpers (replaceChildren with mapped
  array, inline ArrowUp/Down branch, drop the move() helper)
- abort the in-flight fetch from hide() so Escape/blur/outside-click
  cancel the request, and gate the post-await render on
  ctrl.signal.aborted to suppress responses that settle after hide()
- rename idx → index
- restore the leading comment in web_src/css/modules/search.css that an
  earlier commit on this branch dropped

Co-Authored-By: Claude (Opus 4.7) <noreply@anthropic.com>

web_src/css/modules/search.css

@@ -1,3 +1,5 @@
+/* These are the remnants of the fomantic search module */
+
 .ui.search {
   position: relative;
 }