- 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
- Add FFI wrappers for all EskinDeviceFunc trait methods:
eskin_read_hdw_version, eskin_read_matrix_row/col,
eskin_read_device_config1/2, eskin_write_device_config1/2,
eskin_write_matrix_row/col
- Extract sdk_error_to_code() helper for SdkError -> SdkErrorCode conversion
- Update C header (include/eskin_ffi.h) with new function declarations
- Update Python FFI bindings (example/python/eskin_ffi.py) with new methods
- Update README with Python usage instructions and full FFI interface table
