[fabmax]

Vulkan backend:

• Extract frame output abstraction (FrameOutput) from Swapchain and move per-frame fences into FrameSync, so that the backend can run without a surface / swapchain
• Add HeadlessOutput, which blits the screen pass output into an image and reads it back via per-frame readback buffers (sync or async)
• Make surface, present queue and swapchain extension optional
• Track validation layer errors in Instance (used by render tests)
• Add VkSetup.preferredDeviceType, forceDeviceName substring matching
• Fix device selection falling back to first device instead of first suitable device, skip resolve image with numSamples = 1, fix source layout restore in ImageVk.copyFromImage

Headless window subsystem (platform/headless):

• HeadlessWindowSubsystem with Manual (tests) and Continuous (embedding) frame loops, frame capture / frame listeners, optional fixed time step
• Thread-safe resize and input injection (HeadlessWindow, HeadlessInput)
• Fails with a clear message if used with a non-Vulkan backend

Render tests:

• Headless render test harness comparing frames against reference images, failing on validation errors
• Separate renderTest gradle task (not part of build / desktopTest)
• Manually triggered GitHub workflow running tests on lavapipe