i18n: language picker in the bottom-right corner

Replaces the EN/ES/RU buttons in the Visual Presets dock with a picker
that scales to many languages: a globe button with the current code
next to the POWER UP chip, opening a list of languages named in their
own language with their codes, the current one first and checked. A
search field appears past 8 languages. Keyboard: arrows, Home/End,
Enter/Space, Esc, type-ahead; keys stay in the list while it is open.
Choosing a language still asks before dropping unsaved work, then
reloads. Phones get the globe alone and a full-width sheet; the layout
uses logical properties for right-to-left languages.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/keySetup.test.mjs

@@ -9,9 +9,8 @@ import {
 } from './keySetup.js';
 
 test('setup placement moves the same button only in Cyber and disconnects on teardown', () => {
-  const home = {};
+  const home = { prepend: (node) => { node.parentNode = home; } };
   const chip = { parentNode: home, hidden: true };
-  const root = { parentNode: home, before: (node) => { node.parentNode = home; } };
   let moves = 0;
   const toolbar = { append: (node) => { moves++; node.parentNode = toolbar; } };
   const theme = { dataset: { uiTheme: 'tactical' } };
@@ -28,7 +27,7 @@ test('setup placement moves the same button only in Cyber and disconnects on tea
     documentElement: theme,
     getElementById: () => toolbar,
     defaultView: { MutationObserver: Observer },
-  }, chip, root);
+  }, chip);
   assert.equal(chip.parentNode, home);
   for (const variant of ['cyber', 'operator', 'cyber', 'minimal']) {
     theme.dataset.uiTheme = variant;