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/components/Screen.svelte

@@ -0,0 +1,51 @@
+<script lang="ts">
+  import type { Snippet } from 'svelte';
+  import Header from './Header.svelte';
+  import AdBanner from './AdBanner.svelte';
+
+  // The app-shell layout (all screens): the nav bar grows; the ad strip, content and
+  // optional tab bar pin to the bottom (ad directly above the content). Pass `scroll`
+  // false for screens that own their vertical fit (the game board).
+  let {
+    title,
+    back,
+    menu,
+    tabbar,
+    children,
+    scroll = true,
+  }: {
+    title: string;
+    back?: string;
+    menu?: Snippet;
+    tabbar?: Snippet;
+    children?: Snippet;
+    scroll?: boolean;
+  } = $props();
+</script>
+
+<div class="screen">
+  <Header {title} {back} {menu} />
+  <AdBanner />
+  <main class="content" class:scroll>{@render children?.()}</main>
+  {#if tabbar}
+    <nav class="tabbar">{@render tabbar()}</nav>
+  {/if}
+</div>
+
+<style>
+  .screen {
+    display: flex;
+    flex-direction: column;
+    height: 100%;
+  }
+  .content {
+    flex: 0 1 auto;
+    min-height: 0;
+  }
+  .content.scroll {
+    overflow-y: auto;
+  }
+  .tabbar {
+    flex: 0 0 auto;
+  }
+</style>