smoke_exit42.nx

smoke_exit42.nx -- minimal RV64 sovereign smoke test. Compiles to a 'main' that immediately syscalls exit(42). If the full nxc2 pipeline (lex -> parse -> opt -> regalloc -> riscv) + cross-assemble + cross-link + qemu-riscv64 exec chain works, this binary will exit 42 in any compliant runner. Used by the QEMU verification path documented in docs/SELF_HOST_STATUS.md. The number 42 is recognisable in `echo $?` so test scripts can assert without parsing stdout.