UI rewrite 3rd attempt

examples/README.md

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+# Examples
+
+Each example is a self-contained `crafter-build` project that depends on
+the parent `Crafter.Graphics` via `LocalProject`. To build and run any
+of them:
+
+```bash
+cd examples/<name>
+crafter-build -r
+```
+
+## Index
+
+### [HelloWindow](HelloWindow/)
+Minimum viable program: open a window, run the event loop. No Vulkan
+rendering. Useful as a smoke test for `Device::Initialize` + `Window` +
+the platform backend.
+
+### [VulkanTriangle](VulkanTriangle/)
+Ray-traced single triangle through `vkCmdTraceRaysKHR`. Shows the full
+ray-tracing setup: `DescriptorHeapVulkan` with image and buffer slots,
+`PipelineRTVulkan` from raygen / miss / closesthit SPIR-V, BLAS via
+`Mesh::Build`, TLAS via `RenderingElement3D::BuildTLAS`, direct
+`vkWriteResourceDescriptorsEXT` for swapchain views, `RTPass` on
+`window.passes`. Smallest test of the bindless ray-tracing path.
+
+### [HelloUI](HelloUI/)
+Compute-shader UI demo using all three UI tiers:
+
+- **Tier 3** components: `DrawButton`, `DrawSlider`, `DrawProgressBar`,
+  composed via `Rect::SubRect` for resize-safe layout.
+- **Tier 2** standard shaders: `DispatchQuads` for the background and
+  components, `DispatchCircles` for a cursor-tracking dot,
+  `DispatchText` for the button label (with the FontAtlas wired up to
+  `UIRenderer`).
+- **Tier 1** is available too — any custom `ComputeShader` registered
+  on the same heap can be dispatched alongside the standard ones.
+
+Hit-testing and animation are user code (see the `EventListener`
+subscriptions on `window.onMouseMove` / `onMouseLeftClick`); the
+library does not track widgets or focus.
+
+Drop a TTF in this directory as `font.ttf` before running (the example
+loads it via `Font("font.ttf")`).
+
+### [CustomShader](CustomShader/)
+Tier 1 demo: a user-authored compute shader (`inverse-circle.comp.glsl`)
+running alongside the shipped `drawQuads`. The custom shader inverts RGB
+under each item-circle — exactly the kind of effect attempt #2's closed
+shader couldn't express. Shows:
+
+- Defining your own item POD struct in C++ + matching `std430` struct
+  in GLSL.
+- `#include "../../shaders/ui-shared.glsl"` for the bindless heap
+  declarations + `UIDispatchHeader` push-constant contract.
+- `ComputeShader::Load` for the `.spv`, `UIRenderer::RegisterBuffer`
+  for your SSBO, `FillHeader` to populate the standard prefix, and
+  `UIRenderer::Dispatch` to launch — the same pattern the standard
+  shaders use under the hood.
+- The inter-dispatch SHADER_WRITE → SHADER_READ|WRITE barrier is
+  inserted automatically, so the custom shader sees the colored stripes
+  drawn by the prior `DispatchQuads` and reads/writes the swapchain
+  image safely.