Add macOS Menu Bar Status Indicator

Adds a persistent menu bar icon that shows NanoClaw's running status and lets the user start, stop, or restart the service — similar to how Docker Desktop appears in the menu bar.

macOS only. Requires Xcode Command Line Tools (swiftc).

Phase 1: Pre-flight

Check platform

If not on macOS, stop and tell the user:

This skill is macOS only. The menu bar status indicator uses AppKit and requires swiftc (Xcode Command Line Tools).

Check for swiftc