fix: adapt referral network for Telegram MiniApp safe areas

- Extract useHeaderHeight() hook — single source of truth for header
  height across AppShell, ReferralNetwork, and TicketNotificationBell
- Portal top offset now computed dynamically from TG safe area insets
  instead of hardcoded top-16 (fixes overlap with TG header bar)
- Two-row mobile layout: title + selector on separate rows so dropdown
  gets full width on small screens
- Add MOBILE_HEADER_HEIGHT_PX and DESKTOP_HEADER_HEIGHT_PX to constants
- Fix TicketNotificationBell using hardcoded 45px for all platforms

src/config/constants.ts

@@ -17,6 +17,8 @@ export const UI = {
   RESEND_COOLDOWN_SEC: 60,
   TELEGRAM_HEADER_ANDROID_PX: 48,
   TELEGRAM_HEADER_IOS_PX: 45,
+  MOBILE_HEADER_HEIGHT_PX: 64,
+  DESKTOP_HEADER_HEIGHT_PX: 56,
 } as const;
 
 // API