[monorepo] Update next.js version

Summary:
Updating next everywhere we use it per https://nextjs.org/blog/security-update-2025-12-11

tsconfig changes were made by pnpm install and lint

Test Plan: Check sites operate as normal

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D19200