feat(ui): refine Telegram invite & close UX

- Shared invite links open the Mini App fullscreen (mode=fullscreen), so a
  shared link matches the bot's own fullscreen launch.
- A used or expired invite deep-link now lands the visitor in the lobby with a
  gentle notice pointing at the right bot (@<username>, by service language),
  instead of a red "code invalid/expired" error on the Friends screen.
- The in-game close confirmation is armed only on Telegram mobile clients; on
  desktop (tdesktop/macOS/web) it is skipped, where the "changes may not be
  saved" dialog is just noise (drafts auto-save).

ui/src/lib/telegram.ts

@@ -8,6 +8,7 @@ import type { TelegramThemeParams } from './theme';
 interface TelegramWebApp {
   initData: string;
   initDataUnsafe?: { start_param?: string };
+  platform?: string;
   themeParams?: TelegramThemeParams;
   colorScheme?: 'light' | 'dark';
   isFullscreen?: boolean;
@@ -50,6 +51,19 @@ export function insideTelegram(): boolean {
   return !!w && typeof w.initData === 'string' && w.initData.length > 0;
 }
 
+/**
+ * telegramOpenLink opens a t.me link through the Mini App SDK, so Telegram navigates to
+ * it natively (e.g. a bot chat) rather than spawning an in-app browser tab. Returns false
+ * outside Telegram or when the SDK lacks the method, so the caller can fall back to a plain
+ * window.open.
+ */
+export function telegramOpenLink(url: string): boolean {
+  const w = webApp();
+  if (!w?.openTelegramLink) return false;
+  w.openTelegramLink(url);
+  return true;
+}
+
 /**
  * shareTelegramLink opens Telegram's native "share to a chat" picker for url with a
  * caption, through the Mini App SDK (https://t.me/share/url). Returns false outside
@@ -57,10 +71,7 @@ export function insideTelegram(): boolean {
  * Share API. Works consistently on iOS and Android within Telegram.
  */
 export function shareTelegramLink(url: string, text: string): boolean {
-  const w = webApp();
-  if (!w?.openTelegramLink) return false;
-  w.openTelegramLink(`https://t.me/share/url?url=${encodeURIComponent(url)}&text=${encodeURIComponent(text)}`);
-  return true;
+  return telegramOpenLink(`https://t.me/share/url?url=${encodeURIComponent(url)}&text=${encodeURIComponent(text)}`);
 }
 
 /** TelegramLaunch is the data a Mini App launch carries. */
@@ -156,13 +167,29 @@ export function telegramHaptic(kind: Haptic): void {
 }
 
 /**
- * telegramClosingConfirmation toggles the confirmation Telegram shows when the user
- * swipes the Mini App closed — enabled during an active game so it is not lost by accident.
+ * isMobilePlatform reports whether the Mini App runs on a Telegram mobile client (iOS or
+ * Android), where a stray swipe-down can drop the app. Desktop clients (tdesktop, macOS,
+ * web) report other values and close only on a deliberate window action.
+ */
+function isMobilePlatform(): boolean {
+  const p = webApp()?.platform;
+  return p === 'ios' || p === 'android';
+}
+
+/**
+ * telegramClosingConfirmation toggles the confirmation Telegram shows when the user swipes
+ * the Mini App closed — enabled during an active game so it is not lost by accident. The
+ * guard is only armed on mobile clients: on desktop, closing a window is deliberate and
+ * Telegram surfaces a "changes may not be saved" dialog that is just noise here (drafts
+ * auto-save), so the confirmation is skipped there.
  */
 export function telegramClosingConfirmation(on: boolean): void {
   const w = webApp();
-  if (on) w?.enableClosingConfirmation?.();
-  else w?.disableClosingConfirmation?.();
+  if (on) {
+    if (isMobilePlatform()) w?.enableClosingConfirmation?.();
+  } else {
+    w?.disableClosingConfirmation?.();
+  }
 }
 
 let backHandler: (() => void) | null = null;