Remove dead code found by Periphery on all platforms

Delete declarations that Periphery reports unused on every platform that
compiles them (iOS, macOS, tvOS), including nine views used only by their
own previews. Platform-gated code still used on another platform, device-
only MPV render paths, migration models, CloudKit record names, App
Intents metadata and unused parameters are kept.

Yattee/Views/Settings/PlayerControls/MiniPlayerEditorView.swift

@@ -17,8 +17,7 @@ struct MiniPlayerEditorView: View {
     var body: some View {
         List {
             MiniPlayerPreviewView(
-                buttons: viewModel.miniPlayerButtons,
-                showVideo: showVideo
+                buttons: viewModel.miniPlayerButtons
             )
             .listRowInsets(EdgeInsets())
             .listRowBackground(Color.clear)
@@ -213,7 +212,6 @@ struct MiniPlayerEditorView: View {
 
 private struct MiniPlayerPreviewView: View {
     let buttons: [ControlButtonConfiguration]
-    let showVideo: Bool
 
     private let buttonSize: CGFloat = 28
     private let buttonSpacing: CGFloat = 4

Yattee/Views/Settings/PlayerControls/PlayerControlsPreviewView.swift

@@ -12,7 +12,6 @@ import SwiftUI
 /// A view modifier that applies the controls theme color scheme to preview.
 struct PreviewThemeModifier: ViewModifier {
     let theme: ControlsTheme
-    @Environment(\.colorScheme) private var systemColorScheme
 
     func body(content: Content) -> some View {
         if let forcedScheme = theme.colorScheme {