Plan-tune cathedral T1 (per D16 / Codex outside voice). The 3 bins that back
/plan-tune (question-log, question-preference, developer-profile) previously
ignored GSTACK_STATE_ROOT, so tests that tried to point state at a tempdir
via that env var silently wrote to the real ~/.gstack. Make STATE_ROOT take
precedence over GSTACK_HOME so the cathedral's E2E + unit tests can isolate
cleanly without sledgehammering HOME.
Order of precedence:
GSTACK_STATE_ROOT > GSTACK_HOME > $HOME/.gstack
Matches the existing gstack-paths emission order.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Garry Tan