Adds a new NotifyOSLifecycle RPC and server handler to centralize OS sleep/wake handling, introduces Server.sleepTriggeredDown for coordination, updates client UI to call the new RPC, and adjusts the internal sleep event enum zero-value semantics.
A macOS-specific sleep detection mechanism using IOKit and CoreFoundation via cgo is introduced, with a fallback implementation for unsupported platforms. A public Service wrapper provides an event-driven API translating system sleep/wake events into gRPC calls. The UI client integrates sleep detection to manage connectivity state based on system sleep status.
