fix(ui): also resync an open game on a foreground regain without a stream drop

Closes the residual tail of the previous commit: when the live stream stays
alive across a brief suspend (Telegram/iOS can pause the socket without tearing
it down), an in-game event shed from a full hub buffer is never recovered by
the reconnect refetch (no reconnect) or the open-game poll (it only runs while
the stream is down). Mirror the lobby's focus re-poll: bump app.resync on a
foreground regain that did not drop the stream, and have Game.svelte refetch
the open game once per resync. Also rescues a missed move/game_over after a
suspend. Add a silent-join mock seam + an e2e isolating this path; extend the
ARCHITECTURE §10 fallback note.

ui/src/lib/gateway.ts

@@ -22,7 +22,8 @@ if (isMock && typeof window !== 'undefined') {
   };
   // Drive the auto-match opponent join deterministically from the e2e (the mock otherwise
   // attaches a robot on a timer).
-  (window as unknown as { __mock?: { joinOpponent(): void } }).__mock = {
+  (window as unknown as { __mock?: { joinOpponent(): void; joinOpponentSilently(): void } }).__mock = {
     joinOpponent: () => (gateway as MockGateway).joinPendingOpponent(),
+    joinOpponentSilently: () => (gateway as MockGateway).joinPendingOpponentSilently(),
   };
 }