[UI] Extract SkeletonRow into a reusable component

[bayyubenjamin]

Description
The SkeletonRow component is currently defined internally at the bottom of app/components/Arena.tsx. We want to reuse this loading state in other parts of the application.

Task

1. Create a new file app/components/ui/SkeletonRow.tsx.
2. Move the SkeletonRow code from Arena.tsx to this new file.
3. Export it as a default component.
4. Update Arena.tsx to import the new component.

File Location: app/components/Arena.tsx (Line ~210)

Labels: ui, enhancement, good first issue