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/ui/styles/embed.css

@@ -3,6 +3,7 @@
 body.ui-embed #clean-view-exit,
 body.ui-embed #intel-hud,
 body.ui-embed #key-setup-chip,
+body.ui-embed #corner-actions,
 body.ui-embed #key-setup,
 body.ui-embed #first-run-launcher,
 body.ui-embed #command-dock,