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/anyhit.glsl

@@ -0,0 +1,30 @@
+#version 460
+#extension GL_EXT_ray_tracing : enable
+
+// RTVolume any-hit shader — runs on every candidate sphere hit because
+// the geometry is built non-opaque (BuildProcedural opaque=false) and
+// the instances don't force-opaque. Punches a spherical checkerboard of
+// holes: for half the cells it calls ignoreIntersectionEXT, so the ray
+// passes straight through and the background / spheres behind show
+// through — the visible proof the any-hit path runs. Mirrors
+// anyhit.wgsl on the WebGPU path.
+
+hitAttributeEXT vec2 attribs;
+layout(location = 0) rayPayloadInEXT vec3 hitValue;
+
+void main() {
+    // Object-space hit point on the unit sphere → its normal/direction.
+    vec3 posObj = gl_ObjectRayOriginEXT + gl_ObjectRayDirectionEXT * gl_HitTEXT;
+    vec3 n = normalize(posObj);
+
+    const float PI = 3.14159265;
+    float longitude = atan(n.z, n.x);                 // [-PI, PI]
+    float latitude  = asin(clamp(n.y, -1.0, 1.0));    // [-PI/2, PI/2]
+
+    int cu = int(floor((longitude + PI) / PI * 6.0));
+    int cv = int(floor((latitude + PI * 0.5) / PI * 6.0));
+
+    if (((cu + cv) & 1) == 0) {
+        ignoreIntersectionEXT;   // cut-out cell — see through
+    }
+}