Add local/scripts/cleanup-build.sh - a git-aware cleanup script that
uses 'git ls-files' to whitelist tracked files before deletion.
Prevents the class of cleanup disasters that deleted local recipe
sources and local fork sources.
Update AGENTS.md with the new safe cleanup procedure.
Update CONSOLE-TO-KDE-DESKTOP-PLAN.md to v5.8 with the qtdeclarative
qfeatures.h fix and the new safe cleanup script.
