chore: update metrics server URL to active deployment (#623)

The old livepeer-leaderboard-serverless endpoint is no longer deployed.

Author: rickstaa

.env.example

@@ -13,7 +13,7 @@ NEXT_PUBLIC_GITHUB_LIP_NAMESPACE=adamsoffer
 NEXT_PUBLIC_SUBGRAPH_API_KEY=
 NEXT_PUBLIC_SUBGRAPH_ID=FE63YgkzcpVocxdCEyEYbvjYqEf2kb1A6daMYRxmejYC
 NEXT_PUBLIC_WALLET_CONNECT_PROJECT_ID=
-NEXT_PUBLIC_METRICS_SERVER_URL=https://livepeer-leaderboard-serverless.vercel.app
+NEXT_PUBLIC_METRICS_SERVER_URL=https://leaderboard-serverless.vercel.app
 NEXT_PUBLIC_AI_METRICS_SERVER_URL=https://leaderboard-api.livepeer.cloud
 
 # Optional dev overrides (e.g. Graph Studio sandbox; leave empty in prod)