💥 Broad-Phase Collision Culling Lab: Uniform Grid vs Sweep-and-Prune vs Brute Force Pair Tests

Watch up to 2000 bouncing spheres and count how many pair tests a brute-force, uniform-grid or sweep-and-prune broad phase needs per step, while all three find exactly the same contacts. Includes a scaling sweep with fitted growth exponents, grid-cell tuning and a panel of independent numerical checks.