A fresh setup points METADATA_PATH at a synthetic 0.0.0 stub, so the
post-lock recheck could never report current: two concurrent fresh
setups both ran kpackagetool -i instead of the loser reporting the
winner's install. Read the installed metadata once it may exist.

Docs: no guide changes; docs/development.md already promises that a
release installed by another run reports current, and the code now
honors it for fresh installs too. TODO is unaffected.