Coral Colony Growth Field: 2D Laplacian Accretion

This is the 2D counterpart to the 3D coral budding simulation, and it reaches the same branching-vs-massive result through a genuinely different computational route. Instead of tracking each polyp's own free-space budding vector, this version solves a scalar light-availability field on a 2D lattice every frame — a discretized Laplace equation with the colony itself acting as an absorbing boundary — and lets new polyps accrete along that field's gradient, the same "Laplacian growth" mechanism behind diffusion-limited-aggregation models of coral skeletons. Tune the field-sharpness (phototropism), crowding radius, current direction and budding rate to watch the same two coral growth forms — open branching versus dense encrusting — emerge from a field simulation instead of a vector simulation.