Use menu-style pickers in tvOS settings

Introduce PlatformMenuPicker that wraps short-option pickers in
LabeledContent + .pickerStyle(.menu) on tvOS so they render as a
compact dropdown instead of pushing a full-screen option list. On
iOS/macOS it falls through to a plain Picker, leaving rendering
unchanged.

Applied across Playback, Subtitles, Sidebar, Privacy, and Advanced
settings. Long language lists in PlaybackSettingsView are left as
push-style.

Yattee/Views/Settings/AdvancedSettingsView.swift

@@ -99,7 +99,7 @@ struct AdvancedSettingsView: View {
     @ViewBuilder
     private func feedSection(settingsManager: SettingsManager) -> some View {
         Section {
-            Picker(selection: Binding(
+            PlatformMenuPicker(selection: Binding(
                 get: { settingsManager.feedCacheValidityMinutes },
                 set: { settingsManager.feedCacheValidityMinutes = $0 }
             )) {
@@ -192,7 +192,7 @@ struct AdvancedSettingsView: View {
     private var mpvSection: some View {
         if let settingsManager = appEnvironment?.settingsManager {
             Section {
-                Picker(selection: Binding(
+                PlatformMenuPicker(selection: Binding(
                     get: { settingsManager.mpvBufferSeconds },
                     set: { settingsManager.mpvBufferSeconds = $0 }
                 )) {