Add a loading skeleton while leaderboard data fetches

[Muskankr]

Currently there's no visible loading state before the error/content appears. Add a skeleton matching the eventual chart/list layout.

Acceptance criteria:
Skeleton shown immediately on page load/track switch while fetching
Replaced smoothly once data (or the error/empty state) resolves

[SohammPawarr]

Hi @Muskankr, I'd love to work on this issue—could you please assign it to me?
I plan to build a Skeleton component with CSS pulse animations that exactly mimics the leaderboard layout.
I will implement an isLoading state that triggers true during the initial page load and track switches.
The UI will conditionally render this skeleton component while the data fetch request is pending.
Once the data resolves or errors out, I'll set isLoading to false in the finally block for a smooth swap.