Install the touch-target mode at app root and reflect it onto
<html data-touch>. auto removes the attribute so the
(any-pointer: coarse) media query derives the floor; on / off
pin it. The reflector is an effect (not afterNextRender) so it
re-runs on every runtime injectTouchTargets().set(...); the DOM
write is wrapped in untracked() per the signal-architecture rules.