TASK 3 milestone 1: webcam capture (MediaCapture CPU-first, CameraManager refcount, picker, clip/mirror, schema v2, tests)

Services/VideoFrame.cs

@@ -0,0 +1,22 @@
+namespace ytLive.Services;
+
+/// <summary>
+/// A normalized CPU frame (32bpp BGRA, tightly packed). The capture path hands
+/// these to the UI thread, which copies them into the shared WriteableBitmap.
+/// Deliberately the only pixel type the rest of the app knows about — every
+/// future capture source (screen, background-removed webcam) feeds the same seam.
+/// </summary>
+public sealed class VideoFrame
+{
+    public int Width { get; }
+    public int Height { get; }
+    public byte[] BgraPixels { get; }
+    public int Stride => Width * 4;
+
+    public VideoFrame(int width, int height, byte[] bgraPixels)
+    {
+        Width = width;
+        Height = height;
+        BgraPixels = bgraPixels;
+    }
+}