examples/snake: ncurses snake demo

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.

examples/snake/Makefile

@@ -0,0 +1,16 @@
+# examples/snake — built with the ww toolchain only (6c → 6a → 6l).
+#
+# `ww build` does the whole pipeline. -l ncurses -l c routes through
+# 6l's dynamic linker (PT_INTERP + PT_DYNAMIC + PLT/GOT), so the
+# resulting binary maps libncurses.so.6 + libc.so.6 at runtime via
+# the system loader. No cc.
+
+WW := $(shell cd ../..; pwd)/out/bin/ww
+
+snake: snake.ww
+	$(WW) build snake.ww -L /usr/lib -l ncurses -l c
+
+clean:
+	rm -f snake snake.o snake.s snake.combined.ww
+
+.PHONY: clean