Add a default image for users without a profile picture

### Pre-Flight checklist - [x] Did you check to see if this issue already exists? - [x] This is a single feature request. (Do not put multiple feature requests in one issue) - [x] This is not a question or discussion. (Use https://lemmy.ml/c/jerboa for that) ### Describe The Feature Request Below The app currently doesn't display a default profile picture when the user doesn't have it. I believe it makes the navigation a little confusing. I've already coded it, I used the ic_jerboa.xml as the default image, which looks like this: <img width="441" height="215" alt="Image" src="https://github.com/user-attachments/assets/afda06a0-45b5-49c4-b9c0-2a1491ecc4ae" /> Would you guys be ok if I opened the pull request with this change?