Allow dragging the macOS player controls bar to reposition it

The glass controls capsule can now be dragged anywhere over the video.
Position is stored as a fraction of the container size so it survives
window resizes and aspect-ratio driven sheet resizes, persists across
sessions via SettingsManager, and snaps back magnetically when dropped
near the default bottom-center spot. Travel is clamped so the capsule
stays inside the player and never overlaps the top button row. A
mouseDownCanMoveWindow=false backing view keeps the window's
movable-by-background behavior from swallowing the drag.

Yattee/Core/SettingsManager.swift

@@ -74,6 +74,8 @@ final class SettingsManager {
     #if os(macOS)
     var _macPlayerSeparateWindow: Bool?
     var _macPlayerFloating: Bool?
+    var _macControlsBarOffsetX: Double?
+    var _macControlsBarOffsetY: Double?
     var _playerSheetAutoResize: Bool?
     #endif
 
@@ -460,6 +462,8 @@ final class SettingsManager {
         #if os(macOS)
         _macPlayerSeparateWindow = nil
         _macPlayerFloating = nil
+        _macControlsBarOffsetX = nil
+        _macControlsBarOffsetY = nil
         _playerSheetAutoResize = nil
         #endif
         // miniPlayerShowVideo and miniPlayerVideoTapAction moved to preset