17Rahul05/NBodySim ? reverse-engineered prompt

Build me this NBodySim project so I can run a real time 3D gravity simulation of lots of particles, like little galaxies and star clusters moving around and crashing into each other.

I want it to compile cleanly from CMake on Windows and Linux, use CUDA for the heavy physics work, and OpenGL for the visual output with the glowing space look shown in the README. The simulation should handle gravity, particle merging when they collide, and smooth motion over time, and it should launch into a window where I can watch the particles move in real time.

If anything is missing or the current code needs fixes to build, please clean that up too and make sure the shaders get copied or loaded correctly when it runs. Look up current docs online if you need to, and then make it work end to end.