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/lib/app.svelte.ts

@@ -10,6 +10,7 @@ import { navigate, router } from './router.svelte';
 import { errorKey, localeFrom, setLocale, t, type Locale } from './i18n/index.svelte';
 import { applyReduceMotion, applyTheme, type ThemePref } from './theme';
 import { clearSession, loadPrefs, loadSession, saveSession, savePrefs } from './session';
+import type { BoardLabelMode } from './boardlabels';
 
 export interface Toast {
   kind: 'error' | 'info';
@@ -25,6 +26,7 @@ export const app = $state<{
   theme: ThemePref;
   locale: Locale;
   reduceMotion: boolean;
+  boardLabels: BoardLabelMode;
   localeLocked: boolean;
 }>({
   ready: false,
@@ -35,6 +37,7 @@ export const app = $state<{
   theme: 'auto',
   locale: 'en',
   reduceMotion: false,
+  boardLabels: 'beginner',
   localeLocked: false,
 });
 
@@ -101,6 +104,7 @@ export async function bootstrap(): Promise<void> {
   const prefs = await loadPrefs();
   app.theme = prefs.theme ?? 'auto';
   app.reduceMotion = prefs.reduceMotion ?? false;
+  app.boardLabels = prefs.boardLabels ?? 'beginner';
   applyTheme(app.theme);
   applyReduceMotion(app.reduceMotion);
   if (prefs.locale) {
@@ -163,7 +167,12 @@ export async function logout(): Promise<void> {
 }
 
 function persistPrefs(): void {
-  void savePrefs({ theme: app.theme, locale: app.locale, reduceMotion: app.reduceMotion });
+  void savePrefs({
+    theme: app.theme,
+    locale: app.locale,
+    reduceMotion: app.reduceMotion,
+    boardLabels: app.boardLabels,
+  });
 }
 
 export function setTheme(theme: ThemePref): void {
@@ -184,3 +193,8 @@ export function setReduceMotion(on: boolean): void {
   applyReduceMotion(on);
   persistPrefs();
 }
+
+export function setBoardLabels(mode: BoardLabelMode): void {
+  app.boardLabels = mode;
+  persistPrefs();
+}