The SDL native binding ships via @kmamal/sdl's install-time download
script. As an optionalDependency, npm/npx silently skipped that step on
any hiccup, leaving dist/sdl.node absent — so playtest() failed at runtime
with "Cannot find module '../../dist/sdl.node'" on otherwise-capable
machines (seen on macOS via npx). Moving it to dependencies makes the
binary download part of install/npx hydration, so the playtest window
works out of the box. The playtest try/catch still degrades gracefully if
SDL genuinely can't load on an unsupported arch (server + headless tools
stay up).