Player: mpv logs at warn (v only while probing the render mode), 4xx fails at once, load errors show

The session player asked libmpv for every v-level message all session and
media_kit drains them on the UI thread: a retry storm could freeze the
window. ffmpeg reconnects only on 5xx, bounded. A load that fails before
a duration is known reports once ('can't play this: HTTP error 403 ...').

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/pubspec.yaml

@@ -24,6 +24,7 @@ dependencies:
   image: ^4.9.2
   window_manager: ^0.5.2
   crypto: ^3.0.6
+  ffi: ^2.1.0
   # Drag & drop and clipboard files/images (vendored desktop_drop + pasteboard).
   fox_utils:
     git: