Add Telegram cancellation import functionality with tests and documentation

- Implemented Telegram cancellation parsing logic in `telegramCancellationParser.js`.
- Created unit tests for cancellation parsing in `telegramCancellationParser.test.js`.
- Developed integration tests for Telegram import service in `telegramImport.integration.test.js`.
- Added API tests for Telegram import endpoints in `telegramImportApi.test.js`.
- Introduced service tests for Telegram import logic in `telegramImportService.test.js`.
- Documented the Telegram cancellation import process in `telegram-cancellation-import.md`.
- Built a React component for managing Telegram imports in `TelegramImportPanel.jsx`.

backend/src/services/alertSchedulerService.js

@@ -3,9 +3,9 @@ const CLAIM_DUE_ALERTS_SQL = `
     SELECT a.id
     FROM alerts a
     WHERE a.is_active = true
-      AND a.start_time > a.created_at
+      AND (a.start_time > a.created_at OR a.notification_pending = true)
       AND a.start_time <= CURRENT_TIMESTAMP
-      AND (a.end_time IS NULL OR a.end_time >= CURRENT_TIMESTAMP)
+      AND (a.end_time IS NULL OR a.end_time > CURRENT_TIMESTAMP)
       AND a.notification_sent_at IS NULL
       AND a.notification_attempts < 5
       AND (