fix: react dependency

[Zamiell]

Change Summary

Since React 19.1.0 came out, this plugin gives warnings whenever it is installed. This PR attempts to fix this bug.

PR Checklist

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[tharropoulos]

@Zamiell Have you tested it on both a React 18 and a React 19 app?

[Zamiell]

well we know it works fine on react 18 because it has been working fine for years.
as for react 19, yes, i have tested it on version 19.1.0 and it seems to work fine.
the UI still works as before and there are no errors in the javascript console.
all this PR will do is clean up the superfluous warnings on npm install.
as long as react follows semver (which they do) no minor version should break anything.

[tharropoulos]

[Zamiell]

@tharropoulos Any update on this?

[anaxite]

@Zamiell I thought I'd add an extra pair of eyes here, even though it's been a while :)

1. The semver range you suggest is incorrect. >= 16.8.0 < 20.0.0 or ^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0 would be correct, because <= 19.0.0 doesn't allow anything higher than 19.0.x.
2. DocSearch.tsx uses the bare global JSX.Element in two places. @types/react@19 removed the global JSX namespace, and it moved to React.JSX, which leads to errors like Cannot find namespace 'JSX'. These two places need to start using React.JSX.Element.
3. Other tooling could stand to be updated, including for CI (which doesn't test React 19 at all). For example, .nvmrc still declares Node 16, but React 19 expects 18 and above.