Reflect the video below the hinge in the tabletop layout

The iPhone Duo tabletop layout mirrors every presented frame into the
lower half, blurred and fading out, like a screen standing on a glossy
table. The render view blits a quarter-resolution copy of the display
framebuffer into a ring of IOSurface-backed buffers (no Y flip, so the
surface is already mirrored) and hands it to a CALayer hosted by
MPVReflectionView; the simulator's software renderer feeds the same
layer a flipped CGImage. Off during PiP, for audio-only streams, and
via the new Playback → Foldable → "Reflection Below Video" setting.

Yattee/Services/Player/MPV/MPVSoftwareRenderView.swift

@@ -64,6 +64,15 @@ final class MPVSoftwareRenderView: UIView {
     
     /// Callback when view is added to window (for PiP setup)
     var onDidMoveToWindow: ((UIView) -> Void)?
+
+    /// Mirrored copy of every frame for the tabletop reflection (see `MPVRenderView`).
+    let reflectionLayer = MPVReflectionLayer()
+
+    var isReflectionEnabled = false {
+        didSet {
+            if !isReflectionEnabled { reflectionLayer.clear() }
+        }
+    }
     
     /// Dedicated queue for rendering operations
     private let renderQueue = DispatchQueue(label: "stream.yattee.mpv.software-render", qos: .userInitiated)
@@ -434,6 +443,9 @@ final class MPVSoftwareRenderView: UIView {
             DispatchQueue.main.async { [weak self] in
                 guard let self else { return }
                 self.layer.contents = image
+                if self.isReflectionEnabled {
+                    self.reflectionLayer.displayMirrored(image)
+                }
             }
             
             // Notify on first frame rendered