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.

changelog.d/0000-vue-and-pinia.md

@@ -1,3 +1,11 @@
+- The language picker switches language in place instead of reloading the
+  page. Views re-render; code that publishes translated text words it again
+  through `onLocaleChange` (`src/i18n/index.js`), and `<html lang>`/`dir` and
+  the page's `data-i18n` markup follow. `persistLocale` replaces
+  `persistLocaleAndReload`, and `registerUnsavedWork` and the switch's
+  unsaved-work prompt are removed, since a switch no longer loses anything
+  (samehkhamis, #0000).
+
 - The application views translate their text with `t()` as they render,
   so it follows the active locale; they no longer carry `data-i18n*`
   attributes, and `npm run i18n` rejects those in a Vue template. The boot