macOS Harness v0.2.0

A rebuild of the harness around one helper process. Agents drive Mac apps in the background: the real pointer does not move and no app comes to the front, so the person keeps working beside the agent.

• Read: an app's window as a numbered text tree from the Accessibility API, then only what changed, with a screenshot.
• Act: click, type_text, press_key, set_value, scroll, drag, select_text and menu actions, sent to the target app's process.
• The person stays in charge: the agent is refused in an app the person is using; Escape twice or the menu-bar Stop halts everything until the person resumes.
• No approval prompt by default. The agent's own host app and the system password and Touch ID sheets are always refused. ask_before_first_use = true in the policy file turns prompts back on.
• Any agent: macos-harness install --agent claude|codex|pi|opencode|all writes the skill and turn hooks.

Upgrade from 0.1.x: the old Python-on-stdin commands are gone; run macos-harness install --agent all again.
Rollback: run macos-harness uninstall --agent all first, then install 0.1.2.

Details, proof and risks: #13