could interleave with a sleep/wake event causing out-of-order state
transitions. The mutex now covers the full duration of each handler
including the status check, the Up/Down call, and the flag update.
Note: if Up or Down commands are triggered in parallel with sleep/wake
events, the overall ordering of up/down/sleep/wake operations is still
not guaranteed beyond what the mutex provides within the handler itself.
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.
