docs: 说明 test-qr 的参考实现前置条件

test-qr.mjs 需要一个 npm qrcode 作为对照（仅测试用，非运行时依赖），
但脚本与 README 都没说明如何准备，克隆后直接 npm test 会在这一步失败。
现在脚本直接打印可复制的准备命令，README 中英双语也补充了说明与
QR_ORACLE_DIR 的用法。

README.en.md

@@ -125,6 +125,9 @@ adaptive choice, remove the last three entries of `cordis.patch.yml` (the
 node scripts/build-client.mjs   # generates client.js from src/panel.js + src/qrcode.js
 node scripts/smoke.mjs          # host forwarding contract (HTTP/WS/Host/Origin/cookie/bind failure)
 node scripts/test-qr.mjs        # module-by-module comparison against the npm qrcode reference
+# test-qr.mjs compares against a reference implementation (test-only, never a runtime dep):
+#   mkdir -p /tmp/qr-oracle && cd /tmp/qr-oracle && npm init -y && npm i qrcode@1.5.4
+# elsewhere: QR_ORACLE_DIR=<dir> node scripts/test-qr.mjs
 node scripts/test-client.mjs    # browser contract (slot registration, render, route agreement)
 ```