fix: migrate to Next.js 15

[Copilot]

Upgrades Next.js from 14.2.11 to 15.5.6 and React from 18.3.1 to 19.2.0.

Dependency Updates

• next: 14.2.11 → 15.5.6
• react & react-dom: 18.3.1 → 19.2.0
• @types/react & @types/react-dom: 18.x → 19.2.2
• eslint-config-next: 14.2.11 → 15.5.6
• Added overrides for React types to resolve peer dependency conflicts

Breaking Changes

Async params (Next.js 15)

Route params are now Promise-based and must be awaited:

// Before
export type Props = {
  params: { slug: string[] }
}
export default async function Page({ params }: Props) {
  const slug = params.slug
}

// After
export type Props = {
  params: Promise<{ slug: string[] }>
}
export default async function Page({ params }: Props) {
  const { slug } = await params
}

Files updated:

• src/app/[...slug]/layout.tsx
• src/app/[...slug]/page.tsx

React 19 Type Safety

Fixed stricter TypeScript checks:

• src/components/mdx/Code/Code.tsx - Type assertion for children.props
• src/components/mdx/Img/Img.tsx - Type guard for src parameter

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• fonts.googleapis.com
  • Triggering command: /usr/local/bin/node /home/REDACTED/work/docs/docs/node_modules/next/dist/compiled/jest-worker/processChild.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

This pull request migrates the repository to Next.js 15.

Based on the official Next.js 15 migration guide, the following changes are included:

1. Dependency Upgrades

• next has been upgraded to the latest version (15.x.x).
• react and react-dom have been upgraded to the latest version (19.x.x).
• @types/react and @types/react-dom have been upgraded for TypeScript compatibility.
• eslint-config-next has been upgraded to the latest version.

2. Codemod Execution

The npx @next/codemod@canary upgrade latest command was run to automate most of the migration.

3. Breaking Changes Addressed

• Async APIs: Updated usage of cookies, headers, draftMode, params, and searchParams to be asynchronous, as they are no longer synchronous.
• React 19 Changes:
  • Replaced useFormState with useActionState.
  • Updated usages of useFormStatus to account for new keys.
• Caching Defaults: Reviewed and updated caching behavior, as the default is now 'uncached' for Route Handlers and the Client Router Cache.

4. Configuration

• next.config.js has been reviewed and updated for compatibility with Next.js 15.

This migration aims to bring the project up-to-date with the latest features and improvements in Next.js.

This pull request was created as a result of the following prompt from Copilot chat.

This pull request migrates the repository to Next.js 15.

Based on the official Next.js 15 migration guide, the following changes are included:

1. Dependency Upgrades

• next has been upgraded to the latest version (15.x.x).
• react and react-dom have been upgraded to the latest version (19.x.x).
• @types/react and @types/react-dom have been upgraded for TypeScript compatibility.
• eslint-config-next has been upgraded to the latest version.

2. Codemod Execution

The npx @next/codemod@canary upgrade latest command was run to automate most of the migration.

3. Breaking Changes Addressed

• Async APIs: Updated usage of cookies, headers, draftMode, params, and searchParams to be asynchronous, as they are no longer synchronous.
• React 19 Changes:
  • Replaced useFormState with useActionState.
  • Updated usages of useFormStatus to account for new keys.
• Caching Defaults: Reviewed and updated caching behavior, as the default is now 'uncached' for Route Handlers and the Client Router Cache.

4. Configuration

• next.config.js has been reviewed and updated for compatibility with Next.js 15.

This migration aims to bring the project up-to-date with the latest features and improvements in Next.js.

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