ThePalaceProject / web-patron / 31618302338

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Upgrade Next & React to recent versions (PP-4935) (#181)

## Description

- Upgrade Next.js 15.5 to 16.2 and React 18 to 19.2, with matching
`@types/react*`, `react-is`, and tooling bumps (`@next/bundle-analyzer`,
`@next/eslint-plugin-next`, `@axe-core/react`).
- Stay on webpack via `--webpack` flags (Turbopack is the Next 16
default, but we have a custom webpack config); the custom HTTPS dev
server opts out the same way.
- Migrate SWR 1 to 2: array keys are now passed to fetchers as a single
tuple, so array-key call sites use named fetcher wrappers that
destructure the key. Added a unit test covering the wrapper's argument
forwarding.
- Add an npm override forcing `@nypl/design-system-react-components`
onto the root React; it bundles React 16 as a hard dependency, and React
19 rejects elements created by a foreign React copy.
- Remove unused `react-redux`.
- Apply React 19 type fixes (`React.JSX` namespace, explicit
`RefObject<T | null>`)
- Fix the always-false `REACT_AXE` webpack exclusion in
`next.config.js`.
- Stop tracking the auto-generated `next-env.d.ts` (Next 16 rewrites it
differently for dev vs. build, causing constant churn).

## Motivation and Context

Keeps the app on supported framework versions so we continue receiving
security patches and bug fixes.

[Jira PP-4935]

## How Has This Been Tested?

- Manual testing in local dev environment.
- All tests pass locally.
- [CI
checks](https://github.com/ThePalaceProject/web-patron/actions/runs/31558271081)
pass.

## Checklist:

- N/A - I have updated the documentation accordingly.
- [x] All new and existing tests passed.

296 of 393 branches covered (75.32%)

Branch coverage included in aggregate %.

503 of 584 relevant lines covered (86.13%)

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