Function q1_matvec 

pub fn q1_matvec(
    model: &Arc<CmfModel>,
    idx: usize,
    xs: &[f32],
    rows: usize,
    cols: usize,
    out: &mut [f32],
) -> bool

q1 matvec: raw f32 activations, tile-embedded scales. Metal only for now (wgpu q1 WGSL is queued); false = CPU fallback.