Fix macOS permanent black video after player collapse/expand cycles

In separate-window mode, hide() keeps the ordered-out window's SwiftUI
hierarchy alive (nilling contentViewController crashes AVKit), and its
updateNSView unconditionally re-attached the shared MPVOGLView -
stealing it into a window CoreAnimation never composites. The layer's
silent skip-render fallback then consumed every frame flag, so video
stayed black (climbing vo drops) until app restart.

- Decline stealing the shared view from a visible container into a
  non-visible one; owner-initiated transfers bypass the guard
- Only transfer to containers in visible windows or the window still
  tracked by ExpandedPlayerWindowManager; park the view otherwise and
  reclaim it when a container gains a window
- Log skip-render frame consumption (rate-limited) and track render
  health counters (draws/skips/dropped draws)
- Add a watchdog to the playback stats task that detects a stalled
  video output and re-attaches the view to a visible container
- Don't mount player layouts during zero-size layout passes

Yattee/Views/Player/ExpandedPlayerWindowManager.swift

@@ -36,6 +36,15 @@ final class ExpandedPlayerWindowManager: NSObject {
         playerWindow != nil
     }
 
+    /// The live player window managed by this instance (nil after hide()).
+    /// A window that exists here but isn't visible is mid-presentation or
+    /// hidden for PiP — both valid homes for the shared render view, unlike a
+    /// stale ordered-out window that is no longer tracked. Used by
+    /// MPVContainerNSView when picking a transfer target.
+    var currentPlayerWindow: NSWindow? {
+        playerWindow
+    }
+
     private override init() {
         super.init()
     }