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/app.svelte.ts

@@ -62,6 +62,10 @@ export const app = $state<{
   /** Whether an operator feedback reply awaits the player, for the lobby ⚙️ badge (combined
    *  with friend requests) and the Settings → Info badge. */
   feedbackReplyUnread: boolean;
+  /** Whether to show the "outdated invite link" notice: set when a Telegram deep-link friend
+   *  code is already used/expired, so the visitor lands in the lobby with a gentle pointer to
+   *  the bot instead of a scary error on the Friends screen. */
+  staleInvite: boolean;
   /** Monotonic counter bumped when the app returns to the foreground without the live stream
    *  having dropped. An open game watches it to refetch once, recovering an in-game event shed
    *  from a full hub buffer while suspended (the stream-drop case is covered by streamAlive). */
@@ -83,6 +87,7 @@ export const app = $state<{
   notifications: 0,
   chatUnread: {},
   feedbackReplyUnread: false,
+  staleInvite: false,
   resync: 0,
 });
 
@@ -134,6 +139,11 @@ export function showToast(text: string, kind: Toast['kind'] = 'info'): void {
   toastTimer = setTimeout(() => (app.toast = null), 4000);
 }
 
+/** dismissStaleInvite hides the outdated-invite-link notice (the user acknowledged it). */
+export function dismissStaleInvite(): void {
+  app.staleInvite = false;
+}
+
 /** clearChatUnread resets a game's unread chat-message count (called when its chat is opened). */
 export function clearChatUnread(gameId: string): void {
   if (app.chatUnread[gameId]) app.chatUnread = { ...app.chatUnread, [gameId]: 0 };
@@ -487,17 +497,25 @@ async function routeStartParam(param: string): Promise<void> {
       navigate(`/game/${link.id}`);
       return;
     case 'friendCode':
-      navigate('/friends');
       try {
         const friend = await gateway.friendCodeRedeem(link.code);
+        navigate('/friends');
         showToast(t('friends.added', { name: friend.displayName }));
         void refreshNotifications();
       } catch (err) {
-        // Tapping your own invite link redeems your own code: show a friendly note, not
-        // the scary "can't do that to yourself" error.
-        if (err instanceof GatewayError && err.code === 'self_relation') {
+        const code = err instanceof GatewayError ? err.code : '';
+        if (code === 'self_relation') {
+          // Tapping your own invite link redeems your own code: a friendly note, not the
+          // scary "can't do that to yourself" error.
+          navigate('/friends');
           showToast(t('friends.selfInvite'));
+        } else if (code === 'friend_code_invalid') {
+          // A previously shared link whose single-use, 12h code is already spent or expired:
+          // land in the lobby and gently point at the bot, rather than a red error on Friends.
+          navigate('/');
+          app.staleInvite = true;
         } else {
+          navigate('/friends');
           handleError(err);
         }
       }