Upgrade Next.js from 16.2.6 to 16.3

[absolutepraya]

Summary

Upgrade the web app from Next.js 16.2.6 to the latest 16.3.x release.

The current versions in apps/web/package.json are:

• next: 16.2.6
• @next/bundle-analyzer: 16.2.6

Motivation

Next.js 16.3 includes improvements announced by the Next.js team, including:

• Up to 90% lower memory usage during development
• Faster builds, type checking, and rendering
• Better tooling for AI coding agents
• Custom error boundaries
• Instant Navigations for more SPA-like responsiveness

Release announcement: https://nextjs.org/blog/next-16-3

Scope

• Update next to the latest stable 16.3.x version
• Update @next/bundle-analyzer to the matching version
• Regenerate the lockfile
• Review the Next.js 16.3 release notes for behavior or configuration changes
• Check whether any new features require explicit configuration or code changes
• Verify compatibility with the existing React 19 setup and next.config.mjs

Validation

• Development server starts successfully
• Production build succeeds
• Type checking passes
• Linting and formatting checks pass
• Automated tests pass
• Core authentication and bookmark flows are smoke-tested
• No regressions are introduced in Docker or production builds

Notes

The upgrade should remain focused on framework compatibility. Any larger adoption work for new 16.3 features can be split into separate issues if needed.