Stage 7 polish: app shell + nav + lobby + settings (Parts A/B/C)

- Screen.svelte shell: nav bar grows, ad+content+tabbar pinned bottom (mobile feel)
- AdBanner.svelte + banner.ts rotator (params, mock long/short, linkify); Header CSS chevron + grow; Menu (bigger CSS hamburger); TabBar + HoldConfirm shared components; user-select:none
- Lobby: hide-empty sections, tab order New/Tournaments/Stats, place-based result badges (result.ts)
- Settings: Board style > Labels (beginner/classic/none) + prefs plumbing (boardlabels.ts); i18n keys + ru mirror

ui/src/screens/About.svelte

@@ -1,16 +1,17 @@
 <script lang="ts">
-  import Header from '../components/Header.svelte';
+  import Screen from '../components/Screen.svelte';
   import { t } from '../lib/i18n/index.svelte';
 
   const version = '0.7.0';
 </script>
 
-<Header title={t('about.title')} back="/" />
-<main class="page">
-  <h2>{t('app.title')}</h2>
-  <p>{t('about.description')}</p>
-  <p class="muted">{t('about.version', { v: version })}</p>
-</main>
+<Screen title={t('about.title')} back="/">
+  <div class="page">
+    <h2>{t('app.title')}</h2>
+    <p>{t('about.description')}</p>
+    <p class="muted">{t('about.version', { v: version })}</p>
+  </div>
+</Screen>
 
 <style>
   .page {