Notifications API: support Read/Unread Status

[ChengShi-1]

Overview of the Feature Request
To support the SPA-based Notifications page (which is SPA.Q3 proposal), the Notifications API requires enhancements to support tracking and updating the read/unread status of notifications. The following changes are proposed:

• For Get All Notifications by User this, we need a field displayAsRead which allows the frontend to know which notifications have been read.
• add a new API endpoint to mark a notification as read, to update the read status when a user views a notification.
• get unread Notification count in the header (refer to DataverseHeaderFragment.java

What kind of user is the feature intended for?
(Example users roles: API User, Curator, Depositor, Guest, Superuser, Sysadmin)
API User, SPA

What inspired the request?
SPA.Q3.2025

What existing behavior do you want changed?
Notification api

Any open or closed issues related to this feature request?

• Use Cases for Get Notifications and Delete Notifications dataverse-client-javascript#335
• Account Page: Notifications - UI Integration dataverse-frontend#775