Split macOS player mode into window toggle + floating control

Replace the three-way macOS Player Mode picker (Separate Window /
Floating Window / Inline) with a single 'Play in a separate window'
toggle in Playback settings, and move the always-on-top choice to a
pin button in the player's top bar (window mode only).

Floating was really a transient window property (NSWindow.level), not
a peer of the window/inline structural choice — so it belongs on a live
control, not in Settings. The pin state persists across sessions.

- Replace MacPlayerMode enum with macPlayerSeparateWindow /
  macPlayerFloating bool settings
- Branch runtime presentation and window level off the two bools
- Add pin.fill/pin toggle to MacOSPlayerControlsView top bar
- Update localization; drop obsolete playerMode strings and enum tests

Yattee/Core/Settings/SettingsKey.swift

@@ -45,7 +45,8 @@ enum SettingsKey: String, CaseIterable {
     case resolveShortLinksEnabled
 
     // Platform-specific
-    case macPlayerMode
+    case macPlayerSeparateWindow
+    case macPlayerFloating
     case playerSheetAutoResize
     case listStyle
 
@@ -136,7 +137,8 @@ enum SettingsKey: String, CaseIterable {
     /// in both UserDefaults and iCloud, so each platform family syncs independently.
     var isPlatformSpecific: Bool {
         switch self {
-        case .preferredQuality, .cellularQuality, .allowSoftwareDecodedFormats, .macPlayerMode, .listStyle,
+        case .preferredQuality, .cellularQuality, .allowSoftwareDecodedFormats,
+             .macPlayerSeparateWindow, .macPlayerFloating, .listStyle,
              // Home layout — different UI paradigms per platform
              .homeShortcutOrder, .homeShortcutVisibility, .homeShortcutLayout, .homeShortcutCardStyle,
              .homeShortcutColorfulPalette, .homeShortcutCustomPaletteColors,