feat(ui): app-shell behaviour — restore validation, return-to-lobby, push

- A restored game that no longer exists (cancelled/removed/revoked) drops to
  the lobby with a toast instead of the in-game error state: game-state
  exposes a `notFound` flag and the shell redirects via appScreen.go("lobby").
- Add a visible "return to lobby" control to the in-game header.
- Push/toast deep-links use activeView.select(...) (no URL); fix a latent
  visibility-listener double-install on in-place game switches.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/frontend/src/lib/i18n/locales/ru.ts

@@ -30,6 +30,7 @@ const ru: Record<keyof typeof en, string> = {
 	"game.events.turn_ready.message": "ход {turn} готов",
 	"game.events.turn_ready.action": "открыть",
 	"game.events.signature_failed": "подпись повреждена, переподключение…",
+	"game.events.unavailable.message": "эта игра больше недоступна",
 
 	"login.title": "вход в Galaxy",
 	"login.email_label": "электронная почта",
@@ -119,6 +120,7 @@ const ru: Record<keyof typeof en, string> = {
 	"game.shell.menu.theme_light": "светлая",
 	"game.shell.menu.theme_dark": "тёмная",
 	"game.shell.menu.language": "язык",
+	"game.shell.menu.return_to_lobby": "вернуться в лобби",
 	"game.shell.menu.logout": "выйти",
 	"game.shell.coming_soon": "скоро будет",
 	"game.shell.turn.label": "ход {turn}",