docs/development.md: a new section "A Mac app" after "A Mac-only build for development": what --platform mac-app builds and where the app goes (-o), the bundle's layout, APFS clones or copies, where the save, pso_user.tsv, temporary files, env.txt and the log go, signal forwarding and the alert, why the launcher runs the host as a child process (macOS privacy checks on removable volumes: a launcher that exec'ed dmhost got EPERM on every open on the external drive, signed or not), and signing (ad-hoc or --mac-sign, never the hardened runtime, so no notarization). "A Mac-only build for development" no longer says there is no Mac app. The script's examples get one for --platform mac-app --mac-sign, and a line lists the three --platform values. README.md "Pack an IPA": one line pointing at the Mac app.
Docs only; no test ran for this commit.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
