Distribute the native FaceTime companion through Homebrew

Goal

Make native FaceTime installation and upgrades work like imsg:

brew install <tap>/facetime-companion

The formula should download a signed and notarized release archive rather than compiling native code on the user's Mac.

Scope

• publish versioned macOS companion archives from the canonical public source
• add a Homebrew tap formula with pinned URL and SHA-256
• install the companion on PATH and place any required helper assets in stable locations
• add plugin setup detection for default Homebrew paths
• offer an explicit user-confirmed install, reinstall, or upgrade flow
• preserve a configurable binary path for development and remote-Mac topologies
• add version and capability probing comparable to the iMessage plugin's imsg checks

Acceptance criteria

• clean install, upgrade, reinstall, and uninstall paths are tested
• the plugin provides actionable guidance when Homebrew or the binary is missing
• setup never silently installs or upgrades software
• custom binary paths are not modified
• signatures survive Homebrew extraction and installation
• documentation describes manual and guided installation
• a live call succeeds from a clean Homebrew installation

Dependency

Blocked on a signed and notarized native companion release artifact.