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.

webapp/index.html

@@ -22,8 +22,6 @@
     <div class="error" id="error" hidden></div>
     <div class="access-denied" id="accessDenied" hidden>
       <p>Доступ запрещён.</p>
-      <p class="muted" id="accessDeniedHint">Откройте календарь из Telegram.</p>
-      <p class="debug" id="accessDeniedDebug"></p>
     </div>
   </div>
   <script src="https://telegram.org/js/telegram-web-app.js"></script>