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.

backend/utils/tracking_logger.py

@@ -0,0 +1,84 @@
+"""Per-user rotating audit logger for tracking events."""
+import logging
+import os
+from logging.handlers import RotatingFileHandler
+from config.paths import get_logs_dir
+from models.tracking_event import TrackingEvent
+
+
+# Store handlers per user_id to avoid recreating
+_user_loggers = {}
+
+
+def get_tracking_logger(user_id: str) -> logging.Logger:
+    """
+    Get or create a per-user rotating file logger for tracking events.
+    
+    Args:
+        user_id: User ID for the log file
+        
+    Returns:
+        Logger instance configured for the user
+    """
+    if user_id in _user_loggers:
+        return _user_loggers[user_id]
+    
+    logs_dir = get_logs_dir()
+    os.makedirs(logs_dir, exist_ok=True)
+    
+    log_file = os.path.join(logs_dir, f'tracking_user_{user_id}.log')
+    
+    logger = logging.getLogger(f'tracking.user.{user_id}')
+    logger.setLevel(logging.INFO)
+    logger.propagate = False  # Don't propagate to root logger
+    
+    # Rotating file handler: 10MB max, keep 5 backups
+    handler = RotatingFileHandler(
+        log_file,
+        maxBytes=10 * 1024 * 1024,  # 10MB
+        backupCount=5,
+        encoding='utf-8'
+    )
+    
+    formatter = logging.Formatter(
+        '%(asctime)s | %(message)s',
+        datefmt='%Y-%m-%d %H:%M:%S'
+    )
+    handler.setFormatter(formatter)
+    
+    logger.addHandler(handler)
+    _user_loggers[user_id] = logger
+    
+    return logger
+
+
+def log_tracking_event(event: TrackingEvent) -> None:
+    """
+    Log a tracking event to the user's audit log file.
+    
+    Args:
+        event: TrackingEvent to log
+    """
+    if not event.user_id:
+        # If user was deleted (anonymized), skip logging
+        return
+    
+    logger = get_tracking_logger(event.user_id)
+    
+    log_msg = (
+        f"user_id={event.user_id} | "
+        f"child_id={event.child_id} | "
+        f"entity_type={event.entity_type} | "
+        f"entity_id={event.entity_id} | "
+        f"action={event.action} | "
+        f"points_before={event.points_before} | "
+        f"points_after={event.points_after} | "
+        f"delta={event.delta:+d} | "
+        f"occurred_at={event.occurred_at}"
+    )
+    
+    if event.metadata:
+        metadata_str = ' | '.join(f"{k}={v}" for k, v in event.metadata.items())
+        log_msg += f" | {metadata_str}"
+    
+    logger.info(log_msg)