Install the contrast preference at app root and reflect it onto
<html data-contrast>, driving the higher-contrast token overrides in
contrast-tokens.css. Like the motion reflector, this one removes
the attribute for 'auto' so the OS prefers-contrast: more media
query stays in charge, and sets it for 'more' / 'normal'. The
reflector is an effect (not afterNextRender) so it re-runs on every
runtime injectContrast().set(...); the DOM write is wrapped in
untracked() per the signal-architecture rules.