feat: enhance theme handling and layout components for Telegram Mini App

- Updated theme resolution logic to utilize a shared inline script for consistent theme application across routes.
- Introduced `AppShell` and `ReadyGate` components to manage app readiness and theme synchronization, improving user experience.
- Enhanced `GlobalError` and `NotFound` pages with a unified full-screen layout for better accessibility and visual consistency.
- Refactored CSS to implement safe area insets for sticky headers and content safety, ensuring proper layout on various devices.
- Added unit tests for new functionality and improved existing tests for better coverage and reliability.

webapp-next/src/components/CalendarPage.tsx

@@ -171,7 +171,7 @@ export function CalendarPage({ isAllowed, initDataRaw }: CalendarPageProps) {
     <div className="content-safe mx-auto flex min-h-[var(--tg-viewport-stable-height,100vh)] w-full max-w-[var(--max-width-app)] flex-col bg-background px-3 pb-6">
       <div
         ref={calendarStickyRef}
-        className="sticky top-0 z-10 min-h-[var(--calendar-block-min-height)] bg-background pb-2"
+        className="sticky top-[var(--app-safe-top)] z-10 min-h-[var(--calendar-block-min-height)] bg-background pb-2 touch-pan-y"
       >
         <CalendarHeader
           month={currentMonth}