ASCII fluid cursor

Self-contained: one file, zero dependencies, palette in local --vibeui-cursor-001-* variables. Picks up the theme through light-dark() plus a rule for the .dark class. Inside runs a WebGL fluid simulation following stable fluids: velocity and dye splats at the cursor, advection, divergence, 14 Jacobi pressure iterations, gradient subtraction, dye advection. The fields live in six 180×180 textures and do not depend on the block size; cellSize only sets how coarse the ASCII grain is. Velocity is packed into an RGBA texture with an enc/dec pair, so no float extensions are needed and plain webgl1 is enough. The character is picked by dye density from a glyph atlas drawn once on a 2D canvas. Ink and paper colours are read from empty probe nodes: the shader needs numbers, while the CSS variables hold light-dark(). While the cursor is outside, the field stirs itself (animate) so the catalog card is never dead. Under prefers-reduced-motion the simulation is not stepped and the flicker is off.