The root barrel statically re-exported ./qr, which forced every consumer
to resolve the optional 'lean-qr' peer dep regardless of usage. qr now
lives behind the @valentinkolb/stdlib/qr subpath, matching the existing
pattern used for ./browser, ./solid, and ./bun.

BREAKING CHANGE: callers must now use 'import { qr } from "@valentinkolb/stdlib/qr"'.