Enhance API and configuration for Telegram miniapp

- Added support for CORS origins and a new environment variable for miniapp access control.
- Implemented date validation for API requests to ensure correct date formats.
- Updated FastAPI app to allow access without Telegram initData for local development.
- Enhanced error handling and logging for better debugging.
- Added tests for API functionality and Telegram initData validation.
- Updated README with new environment variable details and testing instructions.
- Modified Docker and Git ignore files to include additional directories and files.

webapp/index.html

@@ -23,6 +23,7 @@
     <div class="access-denied" id="accessDenied" hidden>
       <p>Доступ запрещён.</p>
       <p class="muted">Откройте календарь из Telegram.</p>
+      <p class="debug" id="accessDeniedDebug"></p>
     </div>
   </div>
   <script src="https://telegram.org/js/telegram-web-app.js"></script>