0098147e5c
Document two critical build-system findings: C-7.1: Ad-hoc cleanup scripts deleted tracked sources - Added local/scripts/cleanup-build.sh (git-aware cleanup) - Updated AGENTS.md with safe cleanup procedure C-7.2: qtdeclarative missing qfeatures.h caused division-by-zero - Added cmake --install to properly stage generated headers - Added explicit QT_FEATURE_quick_shadereffect/draganddrop flags - Added safety-net to regenerate qtquick-config.h if empty