Function gradient_spinner 

pub fn gradient_spinner(
    _id: &'static str,
    _theme: &Theme,
    cell_px: f32,
    painter: Painter,
    cx: &mut App,
) -> impl IntoElement

The gradient matrix spinner (working indicator): a 3×3 grid of round cells tinted per row from the sunrise gradient. Each cell pulses opacity once per 750ms period; the per-cell phase follows the “arrow-up” pattern (the pulse enters at the bottom edge and converges toward the top-center cell), so the wave reads as travelling upward.