feat: Implement task and reward tracking feature

- Added tracking events for tasks, penalties, and rewards with timestamps.
- Created new TinyDB table for tracking records to maintain audit history.
- Developed backend API for querying tracking events with filters and pagination.
- Implemented logging for tracking events with per-user rotating log files.
- Added unit tests for tracking event creation, querying, and anonymization.
- Deferred frontend changes for future implementation.
- Established acceptance criteria and documentation for the tracking feature.

feat: Introduce account deletion scheduler

- Implemented a scheduler to delete accounts marked for deletion after a configurable threshold.
- Added new fields to the User model to manage deletion status and attempts.
- Created admin API endpoints for managing deletion thresholds and viewing the deletion queue.
- Integrated error handling and logging for the deletion process.
- Developed unit tests for the deletion scheduler and related API endpoints.
- Documented the deletion process and acceptance criteria.

.gitignore

@@ -5,3 +5,4 @@ backend/test_data/db/rewards.json
 backend/test_data/db/tasks.json
 backend/test_data/db/users.json
 logs/account_deletion.log
+backend/test_data/db/tracking_events.json