wip: uncommitted changes from claude run on issue #3

examples/RTStress/resolve.wgsl

@@ -0,0 +1,7 @@
+// RTStress RESOLVE-stage tonemap: Reinhard + gamma 2.2 over the linear
+// accumulator. Registered as a WebGPURTStage::Resolve shader.
+fn resolve_main(coord: vec2<u32>, hdr: vec4<f32>) -> vec4<f32> {
+    let mapped = hdr.rgb / (hdr.rgb + vec3<f32>(1.0));
+    let g      = pow(mapped, vec3<f32>(1.0 / 2.2));
+    return vec4<f32>(g, 1.0);
+}