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/data/bhoteKoshiEvent.js

@@ -25,7 +25,7 @@ import {
 } from './bhoteKoshiEmbeddedMedia.js';
 import { acquireImageryComparison } from '../maps/imageryComparison.js';
 import { createImagerySplit } from '../ui/imagerySplit.js';
-import { formatDate, t, tn, msg } from '../i18n/index.js';
+import { formatDate, t, tn, msg, onLocaleChange } from '../i18n/index.js';
 import { useBhoteKoshiPanelStore } from '../ui/stores/bhoteKoshiPanel.js';
 import { applicationPinia } from '../ui/vueRuntime.js';
 
@@ -1006,8 +1006,10 @@ export function createBhoteKoshiEventLayer({
   let _panelRefs = null;
   let _panelOwner = null;
   let _panelPublished = '';
-  // The dates and field reports, which stay as they were when the panel opened.
+  // The dates and field reports, which stay as they were when the panel
+  // opened, until a locale change words them again.
   let _panelFixed = null;
+  let _offPanelLocale = null;
   let _splitControl = null;
   let _beforeLayer = null;
   let _afterLayer = null;
@@ -2604,9 +2606,9 @@ export function createBhoteKoshiEventLayer({
       id: 'bhote-koshi-split-line',
       handleClass: 'bhote-koshi-split-handle',
       cssProperty: '--bhote-koshi-split',
-      beforeTitle: imageryEndpointText(event.imagery.before),
-      afterTitle: imageryEndpointText(event.imagery.after),
-      ariaLabel: t('Historical reference and post-event image divider'),
+      beforeTitle: () => imageryEndpointText(event.imagery.before),
+      afterTitle: () => imageryEndpointText(event.imagery.after),
+      ariaLabel: () => t('Historical reference and post-event image divider'),
       formatValueText: (beforePercent, afterPercent) =>
         t(
           'A historical reference {before} percent, B post-event {after} percent',
@@ -2666,6 +2668,19 @@ export function createBhoteKoshiEventLayer({
     });
   }
 
+  /**
+   * Word the panel again in the current locale: fresh records, written by
+   * the same syncs that keep them current.
+   */
+  function relocalizePanel() {
+    if (!_panelRefs || !_event) return;
+    _panelRefs = createPanelRecords(_event);
+    _panelFixed = null;
+    writeCinematicButton();
+    syncPanel();
+    syncPresentationMode();
+  }
+
   function syncCinematicButton() {
     if (writeCinematicButton()) publishPanel();
   }
@@ -3517,6 +3532,8 @@ export function createBhoteKoshiEventLayer({
         ),
       );
       publishPanel();
+      _offPanelLocale?.();
+      _offPanelLocale = onLocaleChange(relocalizePanel);
       syncPresentationMode();
       overlayHost.setVisible(
         BHOTE_KOSHI_OVERLAY_SOURCE_ID,
@@ -3613,6 +3630,8 @@ export function createBhoteKoshiEventLayer({
       panelStore.connect(null);
       panelStore.publish(null);
     }
+    _offPanelLocale?.();
+    _offPanelLocale = null;
     _panelOwner = null;
     _panelRefs = null;
     _panelPublished = '';