Build secure macOS keyboard switcher

[GDemay]

What changed

• adds the native Keybridge macOS menu-bar application
• implements authenticated Bonjour enrollment and encrypted peer commands
• coordinates fenced Magic Keyboard transfers across up to three trusted Macs
• adds retry, recovery, ownership ordering, Keychain trust, and lifecycle hardening
• includes onboarding, settings, accessibility, packaging, diagnostics, CI, and physical acceptance tooling

Why

Apple Magic Keyboard hardware does not provide a native multi-host selector. Keybridge coordinates already paired Macs locally without forwarding keystrokes or deleting Bluetooth pairing records.

Validation

• 48 Swift tests across core, Bluetooth simulation, networking/security, application runtime, and three-peer integration
• strict Swift concurrency and warnings-as-errors release build
• license, secret-pattern, and runtime-dependency policy checks
• reproducible non-signature app bundle verification
• release archive and SHA-256 verification
• multiple independent code, security, reliability, UX, and lifecycle reviews

Release gate

Physical USB-C Magic Keyboard A→B→A/A→B→C→A typed-HID acceptance is intentionally still required. The current artifact is ad-hoc signed for local testing and is not a notarized public release.