A custom hue ring — a conic gradient, not a canvas — with saturation and
brightness sliders beside or under it depending on the tile's shape, sized
for a wall panel and reachable from a keyboard. It publishes [h, s, v] by
default, which is what the reference installation's DMX encoders read, and
`format` switches that to [r, g, b] or "#rrggbb".
`usePublish` moves to its own module so a widget in a file of its own can
reach it without importing `widgets.tsx` back.
stroblme
8224d12c8c