### System details

Intel Core i7-14700KF, NVIDIA GeForce RTX 5060 Ti (GB206), nvidia-utils 610.57.04-1, Omarchy 4.0.1-1, Hyprland 0.56.2-1, Linux 7.1.8-arch1-3, sushi 50.0-1, gtk3 1:3.24.52-1, gst-plugin-gtk 1.28.6-2, gst-plugins-base 1.28.6-2

### What's wrong?

On NVIDIA, pressing space on a video in Nautilus opens the Sushi preview window but no video ever plays. Image previews work fine; video is the broken case.

The GStreamer pipeline never prerolls because `gtkglsink` cannot create a GL context shared with GTK3's:

```text
gstglcontext.c:1330:gst_gl_context_create_thread:<glcontextegl0> Failed to create context
gtkgstglwidget.c:688:gtk_gst_gl_widget_init_winsys: Could not create OpenGL context: Failed to create a OpenGL context: EGL_BAD_CONTEXT
gstgtkglsink.c:270:gst_gtk_gl_sink_start:<gtkglsink0> error: Failed to initialize OpenGL with Gtk
ERROR: pipeline doesn't want to preroll.
```

`SushiMediaBin` does have a fallback path to the software `gtksink`, but it only triggers when `gtkglsink` fails to *construct* or reports a software rasterizer. Here `gtkglsink` constructs fine and only fails later in `gst_gtk_gl_sink_start()`, when the pipeline goes to `PAUSED`, so the fallback is never reached and the preview stays blank.

This is not the missing-codecs case in #8475 — `gst-libav` and `gst-plugins-bad` are installed here, and the same file decodes and plays fine through the very same pipeline once the GL context problem is removed (see below).

### Steps to reproduce

On an NVIDIA machine:

1. Open Nautilus, select any video file, press space.
2. The preview window opens with the correct title and toolbar, but the video area stays black and never plays.

Minimal reproduction without Nautilus, using the same sink Sushi uses:

```bash
# fails: EGL_BAD_CONTEXT / Failed to initialize OpenGL with Gtk
gst-launch-1.0 playbin uri=file:///path/to/video.mp4 video-sink="glsinkbin sink=gtkglsink"

# works: video plays
GDK_GL=gles gst-launch-1.0 playbin uri=file:///path/to/video.mp4 video-sink="glsinkbin sink=gtkglsink"
```

### Expected behavior

Space-preview plays videos on NVIDIA, as it does on Intel/AMD.

### Cause and suggested fix

GTK3 on Wayland gives NVIDIA a desktop-GL EGL context that gst-gl cannot share, so the shared-context creation returns `EGL_BAD_CONTEXT`. Forcing GTK3 to a GLES context fixes it. `GDK_GL=gles` is the one-line fix and would fit alongside the existing NVIDIA env vars in `default/hypr/nvidia.lua`:

```lua
hl.env("GDK_GL", "gles")
```

Working around it per-user today with a D-Bus service override, verified on this machine — the previewer now plays video and the OpenGL error is gone from the journal:

```ini
# ~/.local/share/dbus-1/services/org.gnome.NautilusPreviewer.service
[D-BUS Service]
Name=org.gnome.NautilusPreviewer
Exec=/usr/bin/env GDK_GL=gles /usr/lib/org.gnome.NautilusPreviewer
```

Happy to send a PR against `default/hypr/nvidia.lua` if that is the preferred place for it.