Extract runtime lifecycle controller from macOS AppDelegate

[techmore]

The current SwiftUI shell is working, but AppDelegate still owns too many responsibilities: launching the runtime, tracking readiness, handling auto-restart, and coordinating browser open behavior.

Next slice:

• Move runtime process launch/stop/restart and readiness polling into a dedicated Swift controller type.
• Keep the menu bar UI and Preferences UI unchanged.
• Preserve the fixed loopback port and browser auto-open contract.
• Keep the nightly eval loop passing after the refactor.

Acceptance criteria:

• AppDelegate only coordinates menu actions and delegates runtime lifecycle behavior.
• The app still opens the browser automatically when the runtime is ready.
• Startup timeout and restart-on-exit behavior remain unchanged.
• ./packaging/macos/bundle.sh and ./scripts/nightly_product_eval.sh --run still pass.