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/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();
   });
 });