webgpu improvements

interfaces/Crafter.Graphics-WebGPUComputeShader.cppm

@@ -36,6 +36,11 @@ export namespace Crafter {
         SampledTexture      = 1,   // sampled texture_2d<f32>, handle is a slot into heap.imageTable
         Sampler             = 2,   // filtering sampler, handle is a slot into heap.samplerTable
         SampledTextureArray = 3,   // sampled texture_2d_array<f32>, handle is a slot into heap.imageTable
+        // read-write storage SSBO (var<storage, read_write> in WGSL). Use
+        // for buffers shaders need to MUTATE — e.g. physics shaders that
+        // integrate node momentum, write brace stress, or output TLAS
+        // instance transforms.
+        BufferReadWrite     = 4,
     };
 
     struct UICustomBinding {