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.ts

@@ -41,6 +41,12 @@ interface TelegramWebApp {
     onClick?: (cb: () => void) => void;
     offClick?: (cb: () => void) => void;
   };
+  SettingsButton?: {
+    show?: () => void;
+    hide?: () => void;
+    onClick?: (cb: () => void) => void;
+    offClick?: (cb: () => void) => void;
+  };
 }
 
 function webApp(): TelegramWebApp | undefined {
@@ -293,6 +299,19 @@ export function telegramDisableVerticalSwipes(): void {
   webApp()?.disableVerticalSwipes?.();
 }
 
+/**
+ * telegramShowSettingsButton reveals Telegram's native Settings button (in the Mini App's ⋮ menu,
+ * Bot API 7.0) and routes its taps to handler. A no-op outside Telegram or on a client predating
+ * the button, so the app's own in-app settings entry stays the primary path. The app registers it
+ * once per launch (Telegram hides the button when the Mini App closes), so there is no offClick.
+ */
+export function telegramShowSettingsButton(handler: () => void): void {
+  const b = webApp()?.SettingsButton;
+  if (!b?.show) return;
+  b.onClick?.(handler);
+  b.show();
+}
+
 /** Haptic is the set of feedbacks the app triggers. */
 export type Haptic = 'select' | 'success' | 'error' | 'warning' | 'light' | 'medium' | 'heavy';