fix(ui): copy GCG to clipboard on Android in-app WebViews

On-device diagnostics from Android Telegram and VK confirmed both expose
no navigator.share AND no navigator.canShare, so the export fell to a Blob
<a download> that those WebViews silently ignore — nothing happened.

pickGcgDelivery is now a 3-way decision: Web Share where available (iOS),
a clipboard copy in an Android in-app WebView (Telegram/VK: no share, dead
download), else a desktop Blob download. shareOrDownloadGcg reports the
outcome so the game shows a "GCG copied" toast; the copy is VKWebAppCopyText
inside VK (which also covers the desktop VK iframe, where navigator.clipboard
is blocked) and navigator.clipboard otherwise.

Unit tests cover the 3-way choice and the copy/failed outcomes; new i18n key
game.gcgCopied (en+ru); docs ARCHITECTURE/FUNCTIONAL(+ru)/UI_DESIGN/TESTING.

ui/src/lib/i18n/en.ts

@@ -310,6 +310,7 @@ export const en = {
 
   'game.exportGcg': 'Export GCG',
   'game.gcgActiveOnly': 'Available once the game is finished.',
+  'game.gcgCopied': 'GCG copied to the clipboard.',
   'game.addFriendShort': 'Add friend?',
   'game.blockShort': 'Block?',