fix(ui): route external links out of the Android VK WebView

The Android VK client's WebView ignores target=_blank and navigates the
Mini App's own window to the target, stranding the player outside the
game with no way back (the dictionary lookup, About/Feedback links, the
ad banner and the bot-link modal fallbacks). vk-bridge 3.x has no method
to open an external URL, so external links are routed through VK's own
leave-VK redirect (vk.com/away.php), which the client intercepts
natively and hands to the system browser.

onExternalLinkClick moves from lib/telegram to a new lib/links that
composes the Telegram and VK routers; iOS and desktop VK open _blank
correctly and are left alone.

ui/src/game/CheckScreen.svelte

@@ -5,7 +5,7 @@
   import { t } from '../lib/i18n/index.svelte';
   import { alphabetLetters } from '../lib/alphabet';
   import { canCheckWord, dictionaryLookupUrl, sanitizeCheckWord } from '../lib/checkword';
-  import { onExternalLinkClick } from '../lib/telegram';
+  import { onExternalLinkClick } from '../lib/links';
   import type { Variant } from '../lib/model';
 
   // Word-check on its own screen: unlimited dictionary lookups, each with a