feat: add core web vitals tracking to umami

[kanerep]

This PR adds core web vitals to umami and will need testing by a team member with access to umami.

I decided to implement this feature because performance is crucial to defillama so I believe this feature gives us additional visibility where performance might be improved.

Changes

• Core Web Vitals (LCP, CLS, INP, etc.) are reported via Next.js’ reportWebVitals hook with a light retry while the self-hosted Umami script loads. Every event lands under the web-vital tag with the route, rating bucket, and key device hints. The thresholds are based on the recommended values: https://web.dev/articles/defining-core-web-vitals-thresholds
• Use Umami’s Events view to filter by metric (e.g. LCP) and bucket (>4000ms) to see where bottlenecks cluster; combining with the built-in path/device filters highlights slow segments quickly.

How to test

1. yarn build and yarn start - this should generate the core web vitals metrics (they do not get exposed on dev builds)
2. check umami to see if web-vital events are being captured

[kanerep]

@mintdart resolved the conflict on this PR. It's good for review when you get some time, cheers.