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.

docs/ARCHITECTURE.md

@@ -771,7 +771,9 @@ pragmas, `8G`/`H8` coordinates, lower-case blanks, `.` pass-throughs, `-TILES`
 exchanges), plus `#note` lines for resignations and timeouts, which the standard
 does not cover. **GCG export is offered only on a finished game** (`game.ErrGameActive`
 otherwise), so an in-progress journal is never leaked mid-play; the client
-shares the `.gcg` file via the Web Share API where available, else downloads it.
+shares the `.gcg` file via the Web Share API where available; an Android in-app WebView
+(Telegram / VK) has no Web Share and silently ignores an `<a download>`, so there it copies the GCG
+text to the clipboard instead (the payload is tiny), and a plain desktop browser downloads the file.
 
 The alphabet-on-the-wire transport does **not** touch this invariant: the live edge
 exchanges alphabet indices, but the persisted journal (and everything derived from it —