Fix tvOS GL render pipeline defects behind A10X IOFence crash

Apple TV 4K 1st gen on tvOS 26 crashes to the home screen with a
"blocked by IOFence" gpuEvent at playback start (#949) and stutters
with a starved demuxer cache (#947). Defensive fixes in the shared
iOS/tvOS OpenGL path:

- Drain in-flight GPU work (glFinish) before destroying the
  renderbuffer, so a pending presentRenderbuffer fence can't hold the
  CAEAGLLayer IOSurface being torn down or reallocated
- Never leave the EAGLContext current on the main thread: framebuffer
  create/destroy and the background glFinish now unbind on exit, and
  setup no longer binds the context on main at all
- Disable retained backing on tvOS; it exists only for iOS PiP frame
  capture and adds per-frame IOSurface fence pressure
- Report swaps to mpv after each present so display-vdrop (the tvOS
  default video-sync) gets swap-timing feedback, matching macOS

Add verbose-gated diagnostics for remote triage: playback stats every
10s (cache fill/rate, dropped frames, hwdec, avsync) and a rate-limited
slow-frame warning in performRender.

Addresses #949 and #947

Yattee/Services/Player/MPV/MPVLogging.swift

@@ -24,6 +24,10 @@ enum MPVLogging {
     private static var _lastCheckTime: UInt64 = 0
     private static let cacheDurationNanos: UInt64 = 1_000_000_000 // 1 second
 
+    /// Whether verbose MPV logging is enabled (cached, safe from any thread).
+    /// Exposed for callers that gate their own logging on the same setting.
+    static var verboseEnabled: Bool { isEnabled() }
+
     /// Check if verbose logging is enabled (cached for performance).
     /// Safe to call from any thread.
     private static func isEnabled() -> Bool {