Generic Profile Picture Generator On DMS Greeter

### Feature Description

In greeter add user (not listed) should have generic user icon & should have some generic icon for users that doesn't have profile photo (Like Name initials ie "AL for Alex Lay")

### Use Case

Better Usability & Easily Able to identify where to click to switch user.

### Compositor(s)

All compositors

### If Other, please specify

_No response_

### Proposed Solution

In greeter add user (not listed) should have generic user icon & should have some generic icon for users that doesn't have profile photo (Like Name initials ie "AL for Alex Lay")

### Alternatives/Existing Solutions

_No response_

No file or test is identified in the issue. Locate the greeter's add-user and profile-photo rendering entry points, then check how users without photos are represented. Done means the add-user entry has a generic icon and users without profile photos show identifiable initials across compositors.

Written by the indexing model from the issue text.