Installing PrivacyFence

This installs PrivacyFence to /Applications and, since it needs an administrator password anyway, also sets it up to run independently of any AI client on this Mac:

• A dedicated _privacyfence system account owns PrivacyFence's data, settings and audit log — so the AI client PrivacyFence governs can no longer read or rewrite them.
• A menu-bar item (PrivacyFence) starts at login, giving you Open Approvals and Open Settings without going through the AI client at all.

This is the change described in this project's ADR 0002 and issue #428. To uninstall PrivacyFence later, run this from Terminal — your data is kept unless you add --purge: sudo /Applications/PrivacyFenceApp.app/Contents/Resources/scripts/macos_privilege_separation.sh uninstall.