bigger buffer, fewer flushes: squeezing out more headroom

- increased raylib batch buffer from 8192 to 32768 vertices
- ~140k entities at 60fps on i5-6500T
- ~40% improvement over default buffer
- fewer GPU flushes per frame
- also added: release workflows for github and forgejo
- added OPTIMIZATIONS.md documenting the journey
- added README, UI panel with FPS display
- heap allocated entity array to support 1 million entities
- per-entity RGB colors