TITLE: Orbital — N-Body Gravity Playground FILE: 030-gravity-sandbox.html === PROMPT (exact prompt used) === Create "Orbital — N-Body Gravity Playground". A full-screen canvas of deep space (#03040a) with a subtle nebula (layered noise gradients in #1b1464 and #5f0f40) and parallax stars. Click and drag to fling a new body: the drag vector sets its velocity, shown as a dotted aiming line with a predicted trajectory that accounts for existing masses. Bodies attract with softened Newtonian gravity, leave glowing fading trails, and merge on collision (conserving momentum and mass, mixing colours) with a flash. Colour and glow reflect mass (small icy blue → large hot orange/white). Presets: "Binary star", "Solar system", "Figure-eight three-body", "Galaxy collision" (hundreds of light particles around two cores). A minimal monospace HUD shows body count, total energy and simulation speed. Controls: mass selector for new bodies, pause, slow motion, trail length, clear, and "follow" (camera tracks the heaviest body). Scroll/pinch to zoom, right-drag or two-finger drag to pan. Use a fixed-timestep velocity-Verlet integrator. SHARED REQUIREMENTS (apply to every page in this 100-page collection): 1. One standalone HTML5 file. All CSS inline in