UNO refactor (stage 1): hub shell with nav rail + internal-scroll panel

Rebuild ScreenShell into a UNO-style app shell: a persistent NavRail (vertical
side rail in landscape, bottom tab bar in portrait — Home/Profile/Shop/Friends/
Leaderboard/Achievements, active highlighted gold) + a content panel that owns
its own scroll so the page never scrolls as a whole and uses the width in
landscape. Reskins all 10 menu screens at once. Transient screens (auth,
matchmaking, room) opt out via hideNav. New nav.home i18n key.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/screens/AuthScreen.tsx

@@ -14,7 +14,7 @@ export function AuthScreen() {
   const done = () => go("online");
 
   return (
-    <ScreenShell>
+    <ScreenShell hideNav>
       <ScreenHeader title={t("auth.title")} />
       <div className="glass rounded-3xl p-6 max-w-md mx-auto">
         <p className="text-center text-cream/60 text-sm mb-5">{t("auth.subtitle")}</p>