Stage 7 (wip): UI shell, libs, mock transport, screens (lobby->game), e2e smoke

- plain Svelte 5 + TS + Vite (no SvelteKit); CSS-token design system (Telegram-ready), hash router, IndexedDB session
- pure libs: domain model, premium/value maps ported from solver, board replay, placement state machine, i18n en/ru
- in-memory mock transport + seed data; pnpm start runs lobby->active game->board with no backend
- board: pointer-drag + tap placement, MakeMove (popup / 1s-hold commit), two-state zoom, blank chooser, exchange, hint, word-check, chat
- Playwright smoke (mock) green; svelte-check clean; mock bundle ~37 KB gzip

ui/src/lib/i18n/index.svelte.ts

@@ -0,0 +1,17 @@
+// Reactive i18n layer. The locale is a rune, so any component that calls t()
+// re-renders when the locale changes. The catalog + lookup are pure (see catalog.ts).
+
+import { translate, type Locale, type MessageKey } from './catalog';
+
+export { errorKey, localeFrom } from './catalog';
+export type { Locale, MessageKey };
+
+export const i18n = $state<{ locale: Locale }>({ locale: 'en' });
+
+export function setLocale(locale: Locale): void {
+  i18n.locale = locale;
+}
+
+export function t(key: MessageKey, params?: Record<string, string | number>): string {
+  return translate(i18n.locale, key, params);
+}