Patch release with CEF/GTK rendering hardening.
Highlights:
- Fill the GtkPicture presenter during resize so the last frame covers new allocations while CEF catches up.
- Harden GDK DMABUF validation and FD lifetime handling.
- Guard stale accelerated paint callbacks after view destroy.
- Avoid GTK sync scheduling deadlocks by reporting schedule failures.
- Add real DMABUF smoke coverage and CI checks.
Verified with go test ./....