fix(avatar): render onError avatars only in client components

AvatarImage is used on server pages via UserAvatarThumbnail but lacked
'use client', so the onError handler on its <img> could not cross the
RSC boundary. /login rendered the error page, hanging the news e2e
journey until the 240s test timeout.

- Mark AvatarImage as a client component like ProfileImage
- Replace inline <img onError> on mod/users server pages with the
  client AvatarImage component

src/components/shared/avatar-image.tsx

@@ -1,3 +1,5 @@
+"use client";
+
 import {
 	type AvatarOptions,
 	avatarImageOnError,