feat(telegram): native SettingsButton opens our Settings screen

Inside the Mini App, reveal Telegram's native Settings button (Bot API 7.0)
and route its taps to the Settings screen — the standard Mini App affordance.
The in-app gear entry stays the primary path (two entry points by design).
No-op outside Telegram or on a client predating the button.

ui/src/lib/app.svelte.ts

@@ -22,6 +22,7 @@ import {
   telegramContentSafeAreaTop,
   telegramSafeAreaInset,
   telegramDisableVerticalSwipes,
+  telegramShowSettingsButton,
   telegramHaptic,
   telegramLaunch,
   type TelegramLaunch,
@@ -647,6 +648,9 @@ export async function bootstrap(): Promise<void> {
     telegramOnEvent('fullscreenChanged', syncTelegramSafeArea);
     // Re-apply the theme live when the user switches Telegram's light/dark mode while the app is open.
     telegramOnEvent('themeChanged', () => syncTelegramTheme());
+    // Telegram's native Settings button (Bot API 7.0) opens our Settings screen; the in-app gear
+    // entry stays the primary path. No-op on clients predating the button.
+    telegramShowSettingsButton(() => navigate('/settings'));
     await bootTelegram(launch);
     app.ready = true;
     return;