simple_query_linux

Linux 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 (contacts/calendar via native backend)
• linux.tracker and linux.xdg extension methods provide diagnostic metadata
• Batch fallback semantics are ordered and sequentialBestEffort, not atomic