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/intersection.glsl

@@ -0,0 +1,32 @@
+#version 460
+#extension GL_EXT_ray_tracing : enable
+
+// RTVolume intersection shader — runs once per AABB the ray enters
+// (VK_RAY_TRACING_SHADER_GROUP_TYPE_PROCEDURAL_HIT_GROUP_KHR). Analytic
+// ray-sphere test: the unit box [-1,1]^3 built by Mesh::BuildProcedural
+// is treated as the bounding volume of a radius-1 sphere centred at the
+// object origin. The object-space ray is NOT normalised (it is
+// worldToObject * worldRay), so the reported t is directly comparable to
+// the world-space ray parameter — solve the quadratic with the general
+// a = dot(d,d) form rather than assuming |d| == 1. Mirrors
+// intersection.wgsl on the WebGPU path.
+
+hitAttributeEXT vec2 attribs;
+
+void main() {
+    vec3  oc = gl_ObjectRayOriginEXT;          // sphere centre is the origin
+    vec3  d  = gl_ObjectRayDirectionEXT;
+    float a  = dot(d, d);
+    float b  = 2.0 * dot(oc, d);
+    float c  = dot(oc, oc) - 1.0;              // radius 1
+    float disc = b * b - 4.0 * a * c;
+    if (disc < 0.0) return;
+
+    float sq = sqrt(disc);
+    float t  = (-b - sq) / (2.0 * a);                       // near root
+    if (t < gl_RayTminEXT) t = (-b + sq) / (2.0 * a);       // fall back to far root
+    if (t < gl_RayTminEXT || t > gl_RayTmaxEXT) return;
+
+    attribs = vec2(0.0);
+    reportIntersectionEXT(t, 0u);
+}