add react 19 to peer dependencies

when trying to install @apollo/sandbox on a react 19 project, I get a peer dependency error
```
npm error While resolving: @apollo/sandbox@2.7.3
npm error Found: react@19.2.0
npm error node_modules/react
npm error Could not resolve dependency:
npm error peerOptional react@"^16.8.0 || ^17.0.0 || ^18.0.0" from @apollo/sandbox@2.7.3
npm error node_modules/@apollo/sandbox
npm error @apollo/sandbox@"^2.7.3" from the root project
```

we need to add react 19 to the peer dependency for this package

Locate the @apollo/sandbox package metadata and inspect its peerDependencies, then check the existing package validation or install workflow. Done means React 19 is accepted as a peer dependency and the reported npm installation no longer produces the peer dependency error.

Written by the indexing model from the issue text.