fix(LocaleSelector): use closest <a> for hreflang (#221)

# Changes

#182 [introduced elements within the locale selector
links](https://github.com/voorhoede/head-start/pull/182/files#diff-312432278fd76f34872189b8e676a79dd41e5abfe02c5f6fecb834c2abe399efR39),
causing the client-side script to break as it could no longer get the
`hreflang`. This in turn caused the `HEAD_START_LOCALE` cookie not to be
set.

This change fixes this by ensuring it always finds the closest <a> tag
first.

# Associated issue

N/A (found this bug testing upgrade to Astro v5)

# How to test

1. Open preview link
2. Switch locale using the locale selector
3. Verify the `HEAD_START_LOCALE` cookie contains the new value
4. Navigate to the root URL `/` again
5. Verify you're redirected to the locale you switched to before

# Checklist

- [x] I have performed a self-review of my own code
- [x] I have made sure that my PR is easy to review (not too big,
includes comments)
- ~I have made updated relevant documentation files (in project README,
docs/, etc)~
- ~I have added a decision log entry if the change affects the
architecture or changes a significant technology~
- ~I have notified a reviewer~ (minor change, self-reviewed to speed
things up)

<!-- Please strike through and check off all items that do not apply
(rather than removing them) -->

src/components/LocaleSelector/LocaleSelector.client.ts

@@ -1,19 +1,16 @@
 import { cookieName } from '../../lib/i18n';
 
 class LocaleSelector extends HTMLElement {
-  constructor() {
-    super();
+  connectedCallback() {
     this.addEventListener('click', (event: MouseEvent) => {
-      const target = event.target as HTMLAnchorElement;
-      if (!target || target.tagName !== 'A') {
-        return;
-      }
-      if (!target.hreflang) {
+      const target = event.target as HTMLElement;
+      const anchor = target?.closest('a');
+      if (!anchor?.hreflang) {
         console.warn('LocaleSelector: missing required hreflang attribute', { target });
         return;
       }
       // set the hreflang cookie to the selected locale:
-      document.cookie = `${cookieName}=${target.hreflang}; path=/`;
+      document.cookie = `${cookieName}=${anchor.hreflang}; path=/`;
     });
   }
 }