fix: handle 404 errors gracefully in avatar download job (#13491)

## Description

Fixes `Avatar::AvatarFromUrlJob` logging 404 errors as ERROR when
avatars don't exist

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)


## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Small logging-only behavior change that doesn’t affect attachment flow
or persisted data beyond existing sync-attribute updates.
> 
> **Overview**
> Updates `Avatar::AvatarFromUrlJob` error handling to treat
`Down::NotFound` (404/missing avatar URL) as a non-error: it now logs an
INFO message instead of logging as ERROR.
> 
> Other `Down::Error` failures continue to be logged as ERROR, and the
job still runs `update_avatar_sync_attributes` in `ensure`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
675f41041ae3dd4ead6e0dee5f1586dcad9750cd. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

app/jobs/avatar/avatar_from_url_job.rb

@@ -27,7 +27,9 @@ class Avatar::AvatarFromUrlJob < ApplicationJob
       content_type: avatar_file.content_type
     )
 
-  rescue Down::NotFound, Down::Error => e
+  rescue Down::NotFound
+    Rails.logger.info "AvatarFromUrlJob: avatar not found at #{avatar_url}"
+  rescue Down::Error => e
     Rails.logger.error "AvatarFromUrlJob error for #{avatar_url}: #{e.class} - #{e.message}"
   ensure
     update_avatar_sync_attributes(avatarable, avatar_url)