ARVIO vendored-use compatibility note

The bundled qrcode 8.2 upstream metadata requires Python >=3.9.
Arvio Stream uses only the pure-Python PNG QR path. That path is statically
audited against Python 3.8 grammar/common post-3.8 APIs and has a text fallback
if QR import/rendering is unavailable. This is not a claim of upstream Python
3.8 support. Strict upstream-supported QR operation is expected on Python 3.9+.
