fix: align QML import dir priority and drop dead multiarch candidate

- test_qml_hardening.sh prefers the standard /usr/lib/qt6/qml path when present, mirroring the Makefile fallback order, with a regression test for both layouts present. No runtime effect, qmllint tooling only.

- Makefile DEB_HOST_MULTIARCH is empty (not raw uname -m) when dpkg-architecture is absent; the uname -m-linux-gnu candidate already covers that case.
3157dce1d4Simone committed on 9/4/2026, 1:19:22 AMparent4822833

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