test(vulkan-rt): port RTVolume example to native Vulkan (#33)

Regression test for the procedural BLAS path: the same 3x3x3 grid of
unit-box AABBs runs through a PROCEDURAL_HIT_GROUP_KHR group whose GLSL
intersection shader (reportIntersectionEXT) turns each box into a
radius-1 sphere, the any-hit shader punches the spherical-checkerboard
cut-out (visible proof non-opaque geometry runs any-hit), and the
closest-hit shades per-instance tints — the WebGPU example behavior
reproduced natively. Fixed camera in raygen.glsl; the WebGPU/DOM path is
unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/RTVolume/README.md

@@ -1,26 +1,36 @@
 # RTVolume
 
-WebGPU software ray tracing of **procedural (AABB) geometry** with an
-**any-hit** cut-out — the two features added for issue #13.
+Ray tracing of **procedural (AABB) geometry** with an **any-hit** cut-out
+on both backends — software WebGPU (issue #13) and native Vulkan hardware
+RT (issue #33).
 
 A 3×3×3 grid of unit boxes is registered as an AABB BLAS
-(`Mesh::BuildProcedural`, the WebGPU analog of `VK_GEOMETRY_TYPE_AABBS_KHR`).
-The hit group is a `RTShaderGroupType::ProceduralHitGroup` carrying:
+(`Mesh::BuildProcedural` — `VK_GEOMETRY_TYPE_AABBS_KHR` on Vulkan, the
+software AABB-leaf path on WebGPU). The hit group is procedural
+(`RTShaderGroupType::ProceduralHitGroup` /
+`VK_RAY_TRACING_SHADER_GROUP_TYPE_PROCEDURAL_HIT_GROUP_KHR`) carrying:
 
-- `intersection.wgsl` — analytic ray–sphere test that turns each box into a
-  radius-1 sphere (runs in TRACE, once per box the ray enters);
-- `anyhit.wgsl` — returns `RT_ANYHIT_IGNORE` for half the cells of a
-  spherical checkerboard, so the ray passes through and the background /
-  spheres behind show through (the visible proof any-hit runs);
-- `closesthit.wgsl` — normal-based Lambert shading, tinted per instance.
+- `intersection.wgsl` / `intersection.glsl` — analytic ray–sphere test that
+  turns each box into a radius-1 sphere (runs once per box the ray enters);
+- `anyhit.wgsl` / `anyhit.glsl` — ignores the intersection for half the
+  cells of a spherical checkerboard, so the ray passes through and the
+  background / spheres behind show through (the visible proof any-hit runs);
+- `closesthit.wgsl` / `closesthit.glsl` — normal-based Lambert shading,
+  tinted per instance.
 
 The geometry is registered **non-opaque** and the instances clear their
 force-opaque flag, which is what lets the any-hit shader run. Flip the
 instance flag to `kRTGeometryInstanceForceOpaque` (or build the mesh with
 `opaque = true`) to skip any-hit and see solid spheres.
 
-WebGPU/DOM only:
+WebGPU/DOM (free camera, WASD + mouse):
 
 ```
 crafter-build --target=wasm32-wasip1 -r
 ```
+
+Native Vulkan (fixed camera in raygen.glsl):
+
+```
+crafter-build -r
+```