Phase 1: Implement MediaDeviceInfo marshalling & EnumerateDevices

[General-Fault]

Create marshalling infrastructure for DTOs (ValueRange, MediaDeviceInfo, InputDeviceInfo, MediaTrackCapabilities, MediaTrackSettings, enums).

Implement MediaDevices::EnumerateDevices() to query native device list and return Task<IEnumerable>.

Files to modify/create:

• WebRtcInterop/Marshaling/MarshalMedia.h (expand with DTO marshalling)
• WebRtcInterop/Media/MediaDevices.h/cpp (implement EnumerateDevices)
• WebRtcInterop/WebRtcInterop.Shared.vcxitems (add new includes)