Builds a stylised-realistic waterfall in three.js WebGL that pours off a heightfield cliff's true lip into a carved plunge basin — layered parabolic sheets (glassy at the lip, aerated and streaky below, tearing into spray), side threads, a wet ledged rock face, rising spray billboards with a 42° rainbow, ballistic droplets, rings and froth on the pool, and boulders at the foot. Use when the user wants a waterfall, cascade, spring, plunge pool, spray/mist with a rainbow, or water falling off terrain in a three.js / R3F scene.
