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.

.gitea/workflows/ci.yaml

@@ -267,8 +267,8 @@ jobs:
           TELEGRAM_TEST_ENV: "true"
           VITE_TELEGRAM_BOT_ID: ${{ vars.TEST_VITE_TELEGRAM_BOT_ID }}
           VITE_TELEGRAM_LINK: ${{ vars.TEST_VITE_TELEGRAM_LINK }}
-          VITE_TELEGRAM_LINK_EN: ${{ vars.TEST_VITE_TELEGRAM_LINK_EN }}
-          VITE_TELEGRAM_LINK_RU: ${{ vars.TEST_VITE_TELEGRAM_LINK_RU }}
+          VITE_TELEGRAM_GAME_CHANNEL_NAME_EN: ${{ vars.TEST_VITE_TELEGRAM_GAME_CHANNEL_NAME_EN }}
+          VITE_TELEGRAM_GAME_CHANNEL_NAME_RU: ${{ vars.TEST_VITE_TELEGRAM_GAME_CHANNEL_NAME_RU }}
           VITE_GATEWAY_URL: ${{ vars.TEST_VITE_GATEWAY_URL }}
           GATEWAY_DEFAULT_SUPPORTED_LANGUAGES: ${{ vars.TEST_GATEWAY_DEFAULT_SUPPORTED_LANGUAGES }}
           # Unset vars render empty -> the compose ":-" defaults apply.