React 19 drops defaultProps on function components. Converted the 9 of
ours that used it (App, Navigation, ReSendEmail, Reconnect, OAuthLoginButton,
PageHeader, Page, EditDocument, EditSubscription) to destructured default
params; App defaults userId/emailAddress in its withTracker instead (it
spreads {...props} widely). Class components keep defaultProps (still
supported). The only defaultProps warnings left are from the react-share
npm package (CreatedButton/Icon), not our code. REST smoke byte-identical.
react-helmet 5 is unmaintained and breaks under React 18 StrictMode.
Same <Helmet> API in the 15 pages; HelmetProvider wraps <App/> in the
client entry. Browser-verified: per-page titles, meta description and
hreflang alternates all inject. REST smoke byte-identical.
