finishInstall called configureOpencodePermissions unconditionally, causing
fs.mkdirSync + fs.writeFileSync to run even under GSD_TEST_MODE='1', violating
the side-effect-free contract. Guarded the call with !process.env.GSD_TEST_MODE.
Fixes#130
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>