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/lib/nativedialogs.ts

@@ -0,0 +1,24 @@
+// Pure builder for the Telegram native popup (showPopup) used by the deep-link info modals
+// (StaleInviteModal / WelcomeRedeemModal) inside the Mini App. Kept free of the SDK and the DOM so
+// it unit-tests in the node environment; the showPopup transport wrapper lives in telegram.ts and
+// the wiring (native inside Telegram, the in-app Modal elsewhere) in the modal components.
+
+import type { TelegramPopupParams } from './telegram';
+
+/** BOT_BUTTON_ID is the showPopup button id that means "open the bot chat". */
+export const BOT_BUTTON_ID = 'bot';
+
+/**
+ * botInfoPopup builds the native popup for a deep-link info modal: the message with the `{bot}`
+ * token replaced by the `@username` as plain text (a native popup has no inline link, unlike the
+ * in-app Modal), plus an "open bot" button when a username is known and a closing OK button. With
+ * no username it is the message (token removed) and OK only.
+ */
+export function botInfoPopup(title: string, message: string, username: string, okText: string): TelegramPopupParams {
+  const handle = username ? `@${username}` : '';
+  const text = (username ? message.replace('{bot}', handle) : message.replace('{bot}', '').replace('  ', ' ')).trim();
+  const buttons = username
+    ? [{ id: BOT_BUTTON_ID, text: handle }, { id: 'ok', text: okText }]
+    : [{ id: 'ok', text: okText }];
+  return { title, message: text, buttons };
+}