Small interactive demo wired through the new dynamic linker.
Uses libncurses and libc via @symbol bindings; the Makefile
runs the unmodified `ww build` pipeline with -l ncurses -l c
-L /usr/lib. Resulting binary has libncurses.so.6 + libc.so.6
in NEEDED.
Workaround: state struct keeps no array fields and threads the
xs/ys body buffers through main()'s frame, because the current
6c codegen segfaults on `&struct.field`. Once that's fixed the
arrays can move into state and place_food / step / render lose
their *i32 parameters.
