simple_query_macos

macOS platform backend for simple_query.

Current implementation:

• files and media domains: local filesystem query/mutate/observe/binary support
• Restricted domains (messages, calls) return deterministic SimpleQueryErrorCode.notSupported
• contacts and calendar are read-only via native backend
• macos.contacts and macos.calendar extension methods provide diagnostic metadata
• macos.photos uses filesystem fallback and labels those responses accordingly