This is an update to address common agentic issues I run into,
but the `build.nu` script may be generally helpful to people using
the Nix env since `xcodebuild` is broken by default in Nix due to the
compiler/linker overrides Nix shell does.
This updates the Ghostty icon to be compatible with macOS Tahoe
(supports glass effects, light/dark, tinting, etc.). This icon is made
in the new Apple Icon Composer as the source format, and all other
formats are exported from it.
This commit also updates the icon for non-Apple platforms because the
icon is fundamentally the same and I don't see any reason to maintain
multiple icons of fundamentally the same design and style.
This commit also includes updates to the macOS app so that the About
Window and so on will use the new icon.
