Fills the long-empty "内 测 用 户 群" placeholder (was "群二维码 /
邀请链接（待补充）") on the homepage contact grid with the real QQ
group QR (group ID 575404333) plus a scan-or-search line.
Mirrors it across all three READMEs as a scan-to-join block right
after the contact line, rendered from apps/web/public/qq-group.webp
(760×760 QR-only crop with a white quiet zone, ~45KB).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
yuanzonghao
