Refactor Telegram bot and web application for improved functionality

- Disabled the default menu button in the Telegram bot, allowing users to access the app via a direct link.
- Updated the initData validation process to ensure URL-decoded values are used in the data-check string.
- Enhanced error handling in the web application to provide more informative access denial messages.
- Removed unnecessary debug information from the access denied section in the web app.
- Cleaned up the web application code by removing unused functions and improving CSS styles for hidden elements.

main.py

@@ -61,7 +61,8 @@ def _run_uvicorn(web_app, port: int) -> None:
 
 
 def main() -> None:
-    _set_default_menu_button_webapp()
+    # Menu button (Календарь) and inline Calendar button are disabled; users open the app by link if needed.
+    # _set_default_menu_button_webapp()
     app = ApplicationBuilder().token(config.BOT_TOKEN).build()
     register_handlers(app)