Landing v2: icon switchers, ephemeral theme, channel link, drop browser CTA

Owner review-pass rework of the landing page:
- Rename the per-language Telegram link build var
  VITE_TELEGRAM_LINK_EN/_RU -> VITE_TELEGRAM_GAME_CHANNEL_NAME_EN/_RU
  (it carries a channel username; the landing builds https://t.me/<name> --
  the same channels the connector posts to via TELEGRAM_GAME_CHANNEL_ID_*).
- Language switcher -> a globe icon dropdown (flags + names), saved + synced
  to the app prefs.
- Theme switcher -> a sun/moon icon toggle, ephemeral (follows the system
  scheme, no auto, never persisted) -- galaxy-game style.
- Drop the "Play in browser" CTA (no standalone-web onboarding yet).

Docs: FUNCTIONAL(+ru), PLAN, deploy + ui READMEs.

ui/src/lib/i18n/en.ts

@@ -153,7 +153,6 @@ export const en = {
   'about.version': 'Version {v}',
 
   'landing.tagline': 'Play Scrabble with friends or a smart robot — in your browser or on Telegram.',
-  'landing.playWeb': 'Play in browser',
   'landing.playTelegram': 'Play in Telegram',
 
   'lang.en': 'English',

ui/src/lib/i18n/ru.ts

@@ -154,7 +154,6 @@ export const ru: Record<MessageKey, string> = {
   'about.version': 'Версия {v}',
 
   'landing.tagline': 'Играй в Скрэббл с друзьями или умным роботом — в браузере или в Telegram.',
-  'landing.playWeb': 'Играть в браузере',
   'landing.playTelegram': 'Играть в Telegram',
 
   'lang.en': 'English',

ui/src/lib/landing.test.ts

@@ -1,20 +1,20 @@
 import { afterEach, describe, expect, it, vi } from 'vitest';
-import { telegramBotLink } from './landing';
+import { telegramChannelLink } from './landing';
 
-describe('telegramBotLink', () => {
+describe('telegramChannelLink', () => {
   afterEach(() => vi.unstubAllEnvs());
 
-  it('returns the per-language bot link when configured', () => {
-    vi.stubEnv('VITE_TELEGRAM_LINK_EN', 'https://t.me/Scrabble_Game');
-    vi.stubEnv('VITE_TELEGRAM_LINK_RU', 'https://t.me/Erudit_Game');
-    expect(telegramBotLink('en')).toBe('https://t.me/Scrabble_Game');
-    expect(telegramBotLink('ru')).toBe('https://t.me/Erudit_Game');
+  it('builds the per-language t.me link from the channel name', () => {
+    vi.stubEnv('VITE_TELEGRAM_GAME_CHANNEL_NAME_EN', 'Scrabble_Game');
+    vi.stubEnv('VITE_TELEGRAM_GAME_CHANNEL_NAME_RU', '@Erudit_Game'); // a leading @ is tolerated
+    expect(telegramChannelLink('en')).toBe('https://t.me/Scrabble_Game');
+    expect(telegramChannelLink('ru')).toBe('https://t.me/Erudit_Game');
   });
 
-  it('returns null when the locale link is unset or blank', () => {
-    vi.stubEnv('VITE_TELEGRAM_LINK_EN', '');
-    vi.stubEnv('VITE_TELEGRAM_LINK_RU', '   ');
-    expect(telegramBotLink('en')).toBeNull();
-    expect(telegramBotLink('ru')).toBeNull();
+  it('returns null when the locale channel is unset or blank', () => {
+    vi.stubEnv('VITE_TELEGRAM_GAME_CHANNEL_NAME_EN', '');
+    vi.stubEnv('VITE_TELEGRAM_GAME_CHANNEL_NAME_RU', '   ');
+    expect(telegramChannelLink('en')).toBeNull();
+    expect(telegramChannelLink('ru')).toBeNull();
   });
 });

ui/src/lib/landing.ts

@@ -1,16 +1,20 @@
 // Pure helpers for the public landing page (Stage 17), kept out of the Svelte component so
-// the per-language Telegram-bot link selection is unit-testable.
+// the per-language Telegram-channel link selection is unit-testable.
 
 import type { Locale } from './i18n/index.svelte';
 
 /**
- * telegramBotLink returns the t.me link for the locale's game bot, or null when it is not
- * configured. The two links are build-time vars (VITE_TELEGRAM_LINK_EN / VITE_TELEGRAM_LINK_RU)
- * because the test and prod contours run different bots (different usernames), so the link
- * cannot be hardcoded.
+ * telegramChannelLink returns the t.me link for the locale's game channel, or null when it is
+ * not configured. The channel usernames are build-time vars (VITE_TELEGRAM_GAME_CHANNEL_NAME_EN
+ * / VITE_TELEGRAM_GAME_CHANNEL_NAME_RU) because the test and prod contours run different
+ * channels; they are the same channels the connector posts to via TELEGRAM_GAME_CHANNEL_ID_*
+ * (the id to post, the name to link). A leading "@" is tolerated.
  */
-export function telegramBotLink(locale: Locale): string | null {
-  const raw = locale === 'ru' ? import.meta.env.VITE_TELEGRAM_LINK_RU : import.meta.env.VITE_TELEGRAM_LINK_EN;
-  const link = (raw as string | undefined)?.trim();
-  return link ? link : null;
+export function telegramChannelLink(locale: Locale): string | null {
+  const raw =
+    locale === 'ru'
+      ? import.meta.env.VITE_TELEGRAM_GAME_CHANNEL_NAME_RU
+      : import.meta.env.VITE_TELEGRAM_GAME_CHANNEL_NAME_EN;
+  const name = (raw as string | undefined)?.trim().replace(/^@/, '');
+  return name ? `https://t.me/${name}` : null;
 }