Apple graph commands and queries

This release adds a new Apple build graph surface for iOS, macOS, tvOS, and watchOS targets. You can now model Apple targets, capabilities, SDK frameworks, resources, asset catalogs, entitlements, provisioning profiles, and signing in once.toml, then inspect them with the new once query targets, once query capabilities, and once query schema commands. Built-in Apple rules are provided through a Starlark prelude, and once build, once run, and once test can materialize artifacts under .once/out// using the existing action cache and remote execution substrate. A new guide documents the Apple graph model and the available commands.