流：WebGPU 粒子流体

Store particle positions, velocities and affine momentum matrices in GPU storage buffers and allocate a 3D grid buffer. Each frame run compute passes: clear the grid, scatter particle mass and momentum to the 27 neighbouring nodes with quadratic B-spline weights (atomic adds on fixed-point integers), update grid velocities with gravity, boundary conditions and a pointer force, then gather velocities back to particles and advect them. Render particles as instanced small meshes oriented and coloured by velocity, with bloom. three.js TSL compute nodes keep this in JavaScript.