feat(telegram): native dialogs for confirms and deep-link notices

Inside the Mini App, route the destructive confirmations (resign, block, unfriend)
through Telegram's native showConfirm, and present the deep-link info modals (stale
invite, welcome-on-redeem) as a native showPopup whose button opens the bot chat.
Outside Telegram, or on a client predating the dialogs, the existing in-app Modal is
used unchanged; offline also keeps the modal so the action retains its disabled state.

Adds showConfirm/showPopup wrappers to telegram.ts and a pure popup-params builder
(nativedialogs.ts) with unit tests; the deep-link modal components choose native vs
in-app via an effect gated on insideTelegram + dialog availability.

ui/src/components/StaleInviteModal.svelte

@@ -2,7 +2,8 @@
   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 { insideTelegram, telegramDialogsAvailable, telegramOpenLink, telegramShowPopup } from '../lib/telegram';
+  import { BOT_BUTTON_ID, botInfoPopup } from '../lib/nativedialogs';
   import Modal from './Modal.svelte';
 
   // The single bot's @username, for the deep link.
@@ -10,6 +11,10 @@
   // Split the message around the {bot} token so the bot handle renders as an inline link.
   const parts = $derived(t('friends.staleInvite').split('{bot}'));
 
+  // Inside the Mini App with native popups, present the notice as Telegram's own popup instead of
+  // the in-app modal.
+  const useNative = insideTelegram() && telegramDialogsAvailable();
+
   function openBot() {
     if (username) {
       const url = `https://t.me/${username}`;
@@ -19,9 +24,24 @@
     }
     dismissStaleInvite();
   }
+
+  // Native path: raise Telegram's popup when the notice appears; its "open bot" button opens the
+  // bot chat, any other dismissal just clears the notice. The `shown` guard fires it once per notice.
+  let shown = false;
+  $effect(() => {
+    if (!useNative) return;
+    if (app.staleInvite && !shown) {
+      shown = true;
+      void telegramShowPopup(
+        botInfoPopup(t('friends.staleInviteTitle'), t('friends.staleInvite'), username ?? '', t('common.ok')),
+      ).then((id) => (id === BOT_BUTTON_ID ? openBot() : dismissStaleInvite()));
+    } else if (!app.staleInvite) {
+      shown = false;
+    }
+  });
 </script>
 
-{#if app.staleInvite}
+{#if app.staleInvite && !useNative}
   <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>