fix(attribution): use semantic AvatarSize 'xs' for the badge avatar

main refactored ActorAvatar.size from a raw pixel number to the semantic
AvatarSize union (packages/ui/lib/avatar-size). Switch the on-behalf-of badge
avatar from size={14} to size="xs" (16px) after merging main.

Co-authored-by: multica-agent <github@multica.ai>

packages/views/issues/components/attribution-badge.tsx

@@ -96,7 +96,7 @@ export function AttributionBadge({
         name={name}
         initials={initialsOf(name)}
         avatarUrl={initiator.avatar_url}
-        size={14}
+        size="xs"
         className="shrink-0"
       />
       <span className="min-w-0 truncate">