feat(packages): SDK, CLI, MCP, and benchmark clients

One Machine SDK contract across local/self-hosted/managed with typed NotSupported
errors before any network I/O; recovery-grade error taxonomy carrying idempotency
keys; Retry-After-aware backoff; budgeted WebSocket channels. CLI with device
login and OS-keyring credential storage. MCP tools. Benchmark harness with
required-metric completeness gates and regression comparison.