Add tvOS A/V sync diagnostics on its own settings page

Surface audio-delay (±10/±100 ms) and video-sync-mode controls behind an
"A/V Sync" navigation row in Advanced settings rather than inline, keeping the
Advanced page uncluttered. Audio delay applies live to the running MPV
instance; sync mode takes effect on next playback.

Yattee/Models/TVVideoSyncMode.swift

@@ -0,0 +1,29 @@
+//
+//  TVVideoSyncMode.swift
+//  Yattee
+//
+//  MPV `video-sync` mode override exposed on tvOS for A/V sync debugging.
+//
+
+import SwiftUI
+
+enum TVVideoSyncMode: String, CaseIterable, Codable {
+    /// Lock video to display refresh, drop/repeat frames to match. Audio plays at PTS.
+    /// Current shipping default.
+    case displayVdrop = "display-vdrop"
+    /// Lock video to display refresh; resample audio to match. Eliminates A/V drift
+    /// when the display mode doesn't match content fps, at the cost of tiny audio
+    /// pitch correction.
+    case displayResample = "display-resample"
+    /// libmpv default: video adjusts to audio. Most forgiving when display-mode
+    /// matching is uncertain.
+    case audio
+
+    var displayName: LocalizedStringKey {
+        switch self {
+        case .displayVdrop: "settings.playback.tvVideoSyncMode.displayVdrop"
+        case .displayResample: "settings.playback.tvVideoSyncMode.displayResample"
+        case .audio: "settings.playback.tvVideoSyncMode.audio"
+        }
+    }
+}