fix(makefile): stop leaking /var/tmp/solstone-pytest-* dirs
PYTEST_BASETEMP was created at parse time via $(shell mktemp -d ...), so
every make invocation — install, clean, doctor, tab completion — leaked
an empty basetemp dir. Each make test also got its own unique basetemp,
defeating pytest's built-in 3-run rotation and orphaning the contents.
1,109 dirs / 69GB had accumulated.
Move creation into the recipe shell via PYTEST_BASETEMP_INIT (mktemp +
trap) and prepend it to every recipe line that uses
PYTEST_BASETEMP_FLAG. Trap removes the basetemp on EXIT/INT/TERM, so
test runs no longer leak full dirs either.