Switch language in place, without a reload

Choosing a language in the picker now applies it at once. The choice is
stored and ?lang is kept in step through replaceState, and the picker keeps
focus.

Code that writes translated text itself re-presents it on a switch:
onLocaleChange() lets an owner listen, removed at teardown, and status
writers hand over a function of the locale (voice cards, scene director,
SDR, draw hints, imagery split, map sources, Bhote Koshi media) so the
words are rebuilt rather than re-sent. The HUD, cockpit, radio, CCTV,
launch, awareness and credit texts follow the same hook, and
applyDocumentTranslations can be applied again without undoing text code
wrote since.

The unsaved-work registry and persistLocaleAndReload existed only to guard
the reload, so they go, with their catalog entries.

src/creditKeyboard.js

@@ -2,7 +2,7 @@
  * Adds the keyboard semantics omitted by Cesium's href-less attribution links.
  * Cesium retains ownership of showing and hiding its required credit lightbox.
  */
-import { getLocale, t } from './i18n/index.js';
+import { t } from './i18n/index.js';
 
 export function configureCreditKeyboardAccess(root = document) {
   const expand = root?.querySelector?.(
@@ -14,19 +14,19 @@ export function configureCreditKeyboardAccess(root = document) {
   const overlay = lightbox.parentElement;
 
   // Cesium writes these two texts in English once, when it builds the credit
-  // display, and never rewrites them; English keeps Cesium's own text.
-  if (getLocale() !== 'en') {
-    expand.textContent = t('Data attribution');
-    const title = lightbox.querySelector?.('.cesium-credit-lightbox-title');
-    if (title) title.textContent = t('Data provided by:');
-  }
+  // display, and never rewrites them; English is Cesium's own text. Called
+  // again after a locale change, this words them again.
+  expand.textContent = t('Data attribution');
+  const title = lightbox.querySelector?.('.cesium-credit-lightbox-title');
+  if (title) title.textContent = t('Data provided by:');
 
   if (!lightbox.id) lightbox.id = 'cesium-credit-lightbox';
   expand.setAttribute('role', 'button');
   expand.setAttribute('tabindex', '0');
   expand.setAttribute('aria-haspopup', 'dialog');
   expand.setAttribute('aria-controls', lightbox.id);
-  expand.setAttribute('aria-expanded', 'false');
+  if (!expand.hasAttribute?.('aria-expanded'))
+    expand.setAttribute('aria-expanded', 'false');
   close.setAttribute('role', 'button');
   close.setAttribute('tabindex', '0');
   close.setAttribute('aria-label', t('Close data attribution'));