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/telegram.test.ts

@@ -9,6 +9,7 @@ import {
   telegramOpenExternalLink,
   telegramThemeParams,
   telegramSafeAreaInset,
+  telegramShowSettingsButton,
 } from './telegram';
 
 function stubWebApp(initData: string, startParam?: string) {
@@ -77,6 +78,24 @@ describe('telegramOpenExternalLink', () => {
   });
 });
 
+describe('telegramShowSettingsButton', () => {
+  afterEach(() => vi.unstubAllGlobals());
+
+  it('shows the native Settings button and wires its click inside Telegram', () => {
+    const onClick = vi.fn();
+    const show = vi.fn();
+    const handler = vi.fn();
+    vi.stubGlobal('window', { Telegram: { WebApp: { SettingsButton: { onClick, show } } } });
+    telegramShowSettingsButton(handler);
+    expect(onClick).toHaveBeenCalledWith(handler);
+    expect(show).toHaveBeenCalled();
+  });
+
+  it('is a no-op without the SDK button (older client / outside Telegram)', () => {
+    expect(() => telegramShowSettingsButton(() => {})).not.toThrow();
+  });
+});
+
 describe('routeExternalLinkInTelegram', () => {
   afterEach(() => vi.unstubAllGlobals());