Add chore expiry notification system with scheduling and tests

- Implemented `trigger_chore_expiry.py` script to manually trigger chore expiry notifications for users via the admin API.
- Developed `chore_expiry_notification_scheduler.py` to handle the logic for sending notifications for chores expiring within the next 75 minutes.
- Created utility functions in `schedule_utils.py` to determine scheduling and deadlines for chores.
- Added comprehensive tests for the chore expiry notification system in `test_chore_expiry_notification_scheduler.py`, covering various scenarios including scheduled chores, confirmations, and user settings.

backend/api/admin_api.py

@@ -247,3 +247,41 @@ def send_test_digest():
         return jsonify({'items_sent': items_sent}), 200
     except Exception as e:
         return jsonify({'error': str(e), 'code': 'SERVER_ERROR'}), 500
+
+
+@admin_api.route('/admin/test/trigger-chore-expiry', methods=['POST'])
+def trigger_test_chore_expiry():
+    """Trigger the chore expiry notification check for a specific user by email address.
+
+    Only active when DB_ENV is not 'production'. Requires admin authentication.
+    Note: actual push delivery requires VAPID keys to be configured.
+    """
+    if os.environ.get('DB_ENV') == 'production':
+        return jsonify({'error': 'Not found', 'code': 'NOT_FOUND'}), 404
+
+    user_id = get_validated_user_id()
+    if not user_id:
+        return jsonify({'error': 'Unauthorized', 'code': 'UNAUTHORIZED'}), 401
+
+    caller_dict = users_db.get(Query().id == user_id)
+    if not caller_dict or caller_dict.get('role') != 'admin':
+        return jsonify({'error': 'Admin access required', 'code': 'ADMIN_REQUIRED'}), 403
+
+    data = request.get_json() or {}
+    email = data.get('email', '').strip().lower()
+    if not email:
+        return jsonify({'error': 'email is required', 'code': 'MISSING_FIELDS'}), 400
+
+    target = users_db.get(Query().email == email)
+    if not target:
+        return jsonify({'error': 'User not found', 'code': 'USER_NOT_FOUND'}), 404
+
+    target_id = target.get('id')
+    tz_str = target.get('timezone')
+
+    try:
+        from utils.chore_expiry_notification_scheduler import send_chore_expiry_notifications_for_user
+        chores_notified = send_chore_expiry_notifications_for_user(target_id, tz_str)
+        return jsonify({'chores_notified': chores_notified}), 200
+    except Exception as e:
+        return jsonify({'error': str(e), 'code': 'SERVER_ERROR'}), 500