- Separate DeviceState (connection lifecycle) and DeviceMode (Command/Streaming)
- Add stream: Option<StreamRuntime> to EskinDeviceInner
- Wire up start_stream/stop_stream with StreamRuntime (worker thread)
- Add StreamingBusy error for command-mode guard
- Fix stream frame total_len calculation (was double-counting status byte)
- Add ensure_command_mode() check on read_register/write_register
- close() now auto-stops stream if active
- Add stream_demo() in main.rs with Enter-to-stop loop
- Add finger_addr config to StreamConfig
