docs(webgpu-rt): add RTVolume example (procedural spheres + any-hit cut-out)

A 3x3x3 grid of AABB-geometry spheres rendered through an analytic
ray-sphere intersection shader, with an any-hit spherical-checkerboard
cut-out so the background shows through. Exercises both features end to
end on the WebGPU wavefront tracer.

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

examples/RTVolume/project.cpp

@@ -0,0 +1,48 @@
+import std;
+import Crafter.Build;
+namespace fs = std::filesystem;
+using namespace Crafter;
+
+extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> args) {
+    bool isWasm = false;
+    for (std::string_view a : args) {
+        if (a.starts_with("--target=") && a.find("wasm") != std::string_view::npos) {
+            isWasm = true;
+            break;
+        }
+    }
+
+    std::vector<std::string> graphicsArgs(args.begin(), args.end());
+    Configuration* graphics = LocalProject({
+        .projectFile = "../../project.cpp",
+        .args = graphicsArgs,
+    });
+
+    Configuration cfg;
+    cfg.path = "./";
+    cfg.name = "RTVolume";
+    cfg.outputName = "RTVolume";
+    cfg.type = ConfigurationType::Executable;
+    if (isWasm) {
+        cfg.target = "wasm32-wasip1";
+        cfg.defines.push_back({"CRAFTER_GRAPHICS_WINDOW_DOM", ""});
+        cfg.compileFlags.push_back("-msimd128");
+    }
+    ApplyStandardArgs(cfg, args);
+    cfg.dependencies = { graphics };
+
+    std::array<fs::path, 0> ifaces = {};
+    std::array<fs::path, 1> impls = { "main" };
+    cfg.GetInterfacesAndImplementations(ifaces, impls);
+
+    if (isWasm) {
+        cfg.files.emplace_back(fs::path("raygen.wgsl"));
+        cfg.files.emplace_back(fs::path("intersection.wgsl"));
+        cfg.files.emplace_back(fs::path("anyhit.wgsl"));
+        cfg.files.emplace_back(fs::path("closesthit.wgsl"));
+        cfg.files.emplace_back(fs::path("miss.wgsl"));
+        cfg.files.emplace_back(fs::path("resolve.wgsl"));
+        EnableWasiBrowserRuntime(cfg);
+    }
+    return cfg;
+}