The MrGameEng.Sample demo game is deleted along with its assets; the
LittleSim god-sim (which vendors this engine as a submodule) takes over
as the living showcase where every engine feature is demonstrated.
CLAUDE.md, README and docs updated; the demonstration rule now points
to LittleSim, and the stress-scene perf figure is kept as a historical
reference measurement.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>