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/components/StaleInviteModal.svelte

@@ -0,0 +1,53 @@
+<script lang="ts">
+  import { app, dismissStaleInvite } from '../lib/app.svelte';
+  import { t } from '../lib/i18n/index.svelte';
+  import { botUsername } from '../lib/deeplink';
+  import { telegramOpenLink } from '../lib/telegram';
+  import Modal from './Modal.svelte';
+
+  // Point at the bot the player signed in through (its service language), falling back to
+  // the interface locale, so an ru player is sent to the ru bot and an en player to the en one.
+  const username = $derived(botUsername(app.session?.serviceLanguage || app.locale));
+  // Split the message around the {bot} token so the bot handle renders as an inline link.
+  const parts = $derived(t('friends.staleInvite').split('{bot}'));
+
+  function openBot() {
+    if (username) {
+      const url = `https://t.me/${username}`;
+      // Inside Telegram, openTelegramLink navigates to the bot chat natively; elsewhere fall
+      // back to a new tab.
+      if (!telegramOpenLink(url) && typeof window !== 'undefined') window.open(url, '_blank');
+    }
+    dismissStaleInvite();
+  }
+</script>
+
+{#if app.staleInvite}
+  <Modal title={t('friends.staleInviteTitle')} onclose={dismissStaleInvite}>
+    <p class="msg">{parts[0]}{#if username}<button type="button" class="bot" onclick={openBot}>@{username}</button>{/if}{parts[1] ?? ''}</p>
+    <button class="ok" onclick={dismissStaleInvite}>{t('common.ok')}</button>
+  </Modal>
+{/if}
+
+<style>
+  .msg {
+    margin: 0 0 16px;
+    line-height: 1.5;
+  }
+  .bot {
+    background: none;
+    border: none;
+    padding: 0;
+    font: inherit;
+    color: var(--accent);
+    cursor: pointer;
+  }
+  .ok {
+    width: 100%;
+    padding: 10px 12px;
+    border: 1px solid var(--accent);
+    background: var(--accent);
+    color: var(--accent-text);
+    border-radius: var(--radius-sm);
+  }
+</style>