Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments (N/A)
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

I was unable to find an issue or PR which mentions this.

Extensions with non-GitHub repository links always use the GitHub icon,
which is inconsistent with the changes merged in #44738 and #57500. This
change makes `extension_ui.rs` use the Git hosting provider registry to
determine these icons. Below is a preview of the change:

<div align="center">
    <img
        width="450"
        alt="Preview"

src="https://github.com/user-attachments/assets/e35f0eed-de54-48f9-824d-8a5b9bfc596f"
    />
</div>

Release Notes:

- Improved extension repository links to show provider-specific icons.