Implements COM vtable structs for IMMDeviceEnumerator, IMMDevice, IAudioClient, and IAudioRenderClient with correct IUnknown base layout. WasapiDevice handles COM init, default endpoint activation, mix format detection (float/i16), shared-mode Initialize (50ms buffer), and write_samples with GetCurrentPadding/GetBuffer/ReleaseBuffer. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>