[Notifications] Web Push for card charges & transaction comments

Currently, users can customize their notification preferences for transactions and comments, but this is limited to Email and SMS. With the growing adoption of the Web Push API, it would be valuable to give HCB users the ability to receive push notifications directly on their devices.

This would involve...
* Creating a feature flag for web push notifications
* Building out a UI for push notifications, located in the settings page
* Prompting the user for notification access
* Storing notification subscriptions in the database
* Triggering a notification on card charge / transaction comment

Before proceeding, I’d love to get the team's feedback on this potential enhancement. Please share your thoughts below!