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/standalone/application.js

@@ -7,7 +7,12 @@ import { createStandaloneControls } from './controls.js';
 import { createStandaloneData } from './data.js';
 import { createStandaloneTools } from './tools.js';
 import { resolveLocale, applyDocumentLanguage } from '../i18n/locale.js';
-import { applyDocumentTranslations, setLocale } from '../i18n/index.js';
+import {
+  applyDocumentTranslations,
+  getLocale,
+  onLocaleChange,
+  setLocale,
+} from '../i18n/index.js';
 import { mountApplicationViews } from '../ui/views/index.js';
 import { createGoogleTokenSource } from '../maps/googleTokens.js';
 
@@ -31,7 +36,7 @@ export function createStandaloneApplication({
   // and every catalog lookup agree from the first painted frame. Module
   // scripts execute after parsing, so the DOM is ready here: the views
   // translate as they render, and the page's static data-i18n* markup (the
-  // loading screen) is translated once.
+  // loading screen) is translated here and after every language switch.
   const activeLocale = resolveLocale();
   setLocale(activeLocale);
   applyDocumentLanguage(document, activeLocale);
@@ -44,6 +49,13 @@ export function createStandaloneApplication({
   let catalog;
   return createApplication({
     createScene: async (context) => {
+      // A language switch applies in place; the page's own markup follows.
+      context.defer(
+        onLocaleChange(() => {
+          applyDocumentLanguage(document, getLocale());
+          applyDocumentTranslations(document);
+        }),
+      );
       placeSearch = createStandalonePlaceSearch({
         // The bundled city and landmark data the offline name provider reads.
         // The search package takes it as plain data rather than importing it,