Add push notification functionality with tests and digest scheduler

- Implemented push subscription API with tests for subscribing and unsubscribing users.
- Created web push notification tests triggered by child actions.
- Added digest scheduler to send email digests to users at 9 PM local time.
- Developed utility functions for creating and validating digest action tokens.
- Integrated web push sender to handle sending notifications to users.
- Added service worker for handling push notifications in the frontend.
- Created a push opt-in component for user notification preferences.
- Implemented tests for the push opt-in component to ensure correct behavior.
- Updated frontend services to manage push subscriptions and permissions.

backend/api/user_api.py

@@ -46,7 +46,8 @@ def get_profile():
         'first_name': user.first_name,
         'last_name': user.last_name,
         'email': user.email,
-        'image_id': user.image_id
+        'image_id': user.image_id,
+        'email_digest_enabled': user.email_digest_enabled,
     }), 200
 
 @user_api.route('/user/profile', methods=['PUT'])
@@ -58,16 +59,19 @@ def update_profile():
     if not user:
         return jsonify({'error': 'Unauthorized'}), 401
     data = request.get_json()
-    # Only allow first_name, last_name, image_id to be updated
+    # Only allow first_name, last_name, image_id, email_digest_enabled to be updated
     first_name = data.get('first_name')
     last_name = data.get('last_name')
     image_id = data.get('image_id')
+    email_digest_enabled = data.get('email_digest_enabled')
     if first_name is not None:
         user.first_name = first_name
     if last_name is not None:
         user.last_name = last_name
     if image_id is not None:
         user.image_id = image_id
+    if email_digest_enabled is not None:
+        user.email_digest_enabled = bool(email_digest_enabled)
     users_db.update(user.to_dict(), UserQuery.email == user.email)
     
     # Create tracking event
@@ -78,6 +82,8 @@ def update_profile():
         metadata['last_name_updated'] = True
     if image_id is not None:
         metadata['image_updated'] = True
+    if email_digest_enabled is not None:
+        metadata['email_digest_enabled_updated'] = True
     
     tracking_event = TrackingEvent.create_event(
         user_id=user_id,