Update Next.js to 16.3.0

[timneutkens]

Summary

• update the Next.js benchmark app from 16.1.1 to 16.3.0
• update the Next.js starter and matching eslint-config-next to 16.3.0
• refresh both pnpm lockfiles

Verification

• app type-check and Turbopack production build
• starter lint, type-check, and webpack production build
• SSR request throughput benchmark: 360 ops/sec, 0 errors
• SSR load benchmark: 2,007 requests, 0 errors
• client-rendered browser benchmark: 5/5 runs passed
• server-rendered browser benchmark: 5/5 runs passed

[AlexanderKaran]

@timneutkens

Can we hold off on bumping versions until all issues are fixed?

Once you're happy with the current NextJS setup, we will create a PR for each minor and major version between the current version and the latest, and record stats for each.

[AlexanderKaran]

Closing PR and will start bumping versions once NextJS Setups have been signed off