[Feature Request] Show new comment icon directly on Agile Board cards

### Current situation
Currently, notifications about task comments are not visible directly on the Agile Board cards. To check if there are new comments, I have to either open the card or rely on the global notification bar.

### Problem
This behavior makes comment tracking unintuitive, especially when working with many issues at once. It’s easy to miss important updates or waste time opening cards just to see if something new has been posted.

### Proposal
Introduce a small notification icon on each task card within the Agile Board (similar to other optional card icons):

- The icon should appear at the top-right (or optionally bottom-right) corner of the card.  
- If there are new unread comments for that task, the icon is highlighted (e.g., with a different color or simple badge).  
- It’s not necessary to display the exact number of unread comments — a simple indicator is enough to make cards with updates easily identifiable.  

### Expected benefits
- Faster visibility of feedback and discussions directly on the board.  
- Reduced need to constantly open/close cards to check for updates.  
- Improved UX for teams navigating dozens of tasks in Agile view.  

### Technical notes
- The icon should reflect the state “unread comments” for the logged-in user.  
- Ideally, it could reuse the backend logic from the Notification Center to update the card state dynamically.  

Thanks!