macOS Ghostty Application

Use swiftlint for formatting and linting Swift code.
If code outside of this directory is modified, use zig build -Demit-macos-app=false before building the macOS app to update the underlying Ghostty library.
Use build.nu to build the macOS app, do not use zig build (except to build the underlying library as mentioned above).
- Build: build.nu [--scheme Ghostty] [--configuration Debug] [--action build]
- Output: build/<configuration>/Ghostty.app (e.g. build/Debug/Ghostty.app)
Run unit tests directly with build.nu --action test