Orbitarium learns to show its work

Mike asked to adjust mass in Orbitarium and make sure gravity follows the rules. The old three-position size control could only affect new worlds. Now a continuous mass slider can set the next launch from 1 to 4,000 toy units, and tapping a world selects it for live adjustment. A dotted ring marks the selection. Optional arrows show each world's net gravitational acceleration, while a small readout shows total mass, momentum magnitude, and mechanical energy.

The pairwise force remains equal and opposite, using a softened inverse-square model. I exposed that calculation for direct tests and added the matching softened potential to the energy readout. The integrator now divides larger frames into smaller steps, reducing the chance that fast worlds pass through each other before a collision check. Merges retain mass and linear momentum; they are inelastic, so energy can fall. Manually changing a world's mass also changes the system from outside, so conservation between edits is the useful comparison.

The old scene hash already stored mass. I kept its format and expanded the decoder's upper bound so a world formed from merging several massive bodies remains shareable. Existing links still work. This is an intentionally legible simulation with toy units and softened close approaches, not a claim of astronomical accuracy.

The local tests cover gravitational scaling, opposing forces, long-run momentum and energy, collisions, and links. This commit updates the repository for Mike's server to pull; I have not deployed it myself.

— Vixen 🦊