Vendor media_kit_video 2.0.1 with the X11/EGL fix (hardware rendering on X11 with Flutter >= 3.38)

Flutter >= 3.38 keeps its EGL contexts on the raster thread, so
media_kit's video output found none on the platform thread and fell
back to software rendering (no shaders, ~5 fps) on X11. The patched
output opens Flutter's EGL display itself, steps GDK's GLX context aside
on X11 and releases its own context. Patch from a friend's agent, kept
in third_party/media_kit_video/starsync/. Wayland/NVIDIA still renders
on the GPU (checked); the X11 path was verified on the friend's machine.

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

docs/ARCHITECTURE.md

@@ -12,6 +12,7 @@ Plain overview first: [HOW-IT-WORKS.md](HOW-IT-WORKS.md). Wire format:
 | `apps/desktop` | Flutter app: UI, `AppGraph` (composition root), `SyncClient`, `Connection`, `SessionCoordinator`, `Navigation`, `YourServer` (`ServerIsolate`), `MediaPipeline` (opening media), `PlaybackController` (the session player's marks and commands), the player host (`PlayerHost`, `MediaKitHost`: the only media_kit user besides the `Video` widget glue), update UI (`UpdateController`) | ships with `starsync-server` |
 | `tool` | harnesses: `range_logger`, `shaper`, `fake_viewer`, `e2e_check` | dev only |
 | `deploy` | systemd unit for the dedicated server | |
+| `third_party/media_kit_video` | upstream media_kit_video 2.0.1 with Starsync's patches (`starsync/README.md`: Flutter ≥ 3.38 EGL display on the platform thread, the X11 GLX step-aside) | vendored; re-apply patches on update |
 
 Guard: `packages/core/test/flutter_free_test.dart` fails if anything under
 `core/lib` imports Flutter, `dart:ui` or `signals_flutter`; CI runs

docs/DEVELOPMENT.md

@@ -6,7 +6,10 @@ Layout and rules: [ARCHITECTURE.md](ARCHITECTURE.md).
 
 Needs the Flutter SDK (beta channel, Dart 3.13+) and, for the Linux desktop
 build, the usual GTK toolchain (clang, cmake, ninja, pkg-config, libgtk-3-dev).
-mpv libraries come from `media_kit_libs_video`. `flutter_soloud` (the app's
+mpv libraries come from `media_kit_libs_video`. `media_kit_video` is the patched copy in
+`third_party/media_kit_video` (see its `starsync/README.md`); test video
+output changes under X11 (`GDK_BACKEND=x11`, ideally a real X11 session)
+and Wayland. `flutter_soloud` (the app's
 sounds) compiles SoLoud and miniaudio from source in its build hook with
 that C++ toolchain (MSVC on Windows); it needs no audio dev headers (miniaudio
 loads ALSA / PulseAudio / JACK at run time) and, with `no_xiph_libs` set in