refactor: replace Fomantic search module with first-party code (#37443)

- Replace fomantic `search` code with minimal first-party code
- Added a small fix to vertically align search box and search button
- Manually tested all search forms.
- Add `errorName` helper, similar to `errorMessage`.

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

web_src/js/modules/errors.ts

@@ -2,10 +2,16 @@
 import {html} from '../utils/html.ts';
 import type {Intent} from '../types.ts';
 
+/** Extract a message string from an unknown caught value. */
 export function errorMessage(err: unknown): string {
   return (err as Error)?.message || String(err);
 }
 
+/** Extract a name string from an unknown caught value. */
+export function errorName(err: unknown): string {
+  return (err as Error)?.name ?? '';
+}
+
 export function showGlobalErrorMessage(msg: string, msgType: Intent = 'error', details?: string) {
   const parentContainer = document.querySelector('.page-content') ?? document.body;
   if (!parentContainer) {