Improve PiP

Fix #186
Fix #196

macOS/Windows.swift

@@ -47,9 +47,17 @@ enum Windows: String, CaseIterable {
         }
     }
 
+    func hide() {
+        window?.close()
+    }
+
     func toggleFullScreen() {
         window?.toggleFullScreen(nil)
     }
+
+    var visible: Bool {
+        window?.isVisible ?? false
+    }
 }
 
 struct HostingWindowFinder: NSViewRepresentable {