Foundation for hardware video decode in BOTH preview and export: wgpu textures
can't cross devices, and a hardware-decoded frame is a DMA-BUF-imported texture
that needs the import extensions (only addable via wgpu-hal device_from_raw). So
eframe + the compositor + decode + encode must share ONE custom device.
- vk_device::create_windowed(): the existing import-capable DrmDevice plus
VK_KHR_swapchain (the WSI surface instance extensions are already enabled by
Instance::init), for use as the editor's main device.
- main.rs: on Linux, build the shared device and inject it into eframe via
WgpuSetup::Existing (the egui fork supports it); fall back to wgpu's normal
device + software decode on any failure, on other platforms, or via
LB_NO_SHARED_DEVICE. The DrmDevice's wgpu handles are cloned into eframe
(Arc-backed), so the VkDevice persists with them.
Runtime-verified: the editor launches and renders identically (canvas/vello,
video, panels) on the shared device, and the env-var fallback works.
ca612d7807