Drop README-facing visual assets here.

Current README assets:

• demo-terminal.svg — interactive menu/demo capture generated from a real local run
• headless-output.svg — gravity headless output summary generated from a real local run

Recommended next assets:

• demo-terminal.png — raster export if you want a social-preview-friendly variant
• headless-output.png — raster export for platforms with weak SVG rendering
• demo-loop.gif — short animated terminal capture of a scenario running

Guidelines:

• use captures that show motion, structure, and legibility
• prefer output that communicates simulation behavior quickly
• keep terminal themes high-contrast and clean
• use real outputs from the repo, not fabricated mock images