Function smv_kernel_f32 

pub fn smv_kernel_f32(
    nx: usize,
    ny: usize,
    nz: usize,
    vsx: f32,
    vsy: f32,
    vsz: f32,
    radius: f32,
) -> Vec<f32>

Generate SMV kernel in image space (f32 version for WASM performance)

Creates a binary sphere of given radius, normalized so sum = 1. Kernel is centered at index (0, 0, 0) for FFT compatibility.