Fix cold_start: boot to QUIT not KERNEL

cold_start pointed to word_kernel, which calls pill_load/cue before
the setjmp recovery point in QUIT is established. On real hardware
(no QEMU -device loader), this cues garbage at 0x10000000, crashes,
and longjmps into an uninitialized nock_abort — hang, no REPL.

Boot to word_quit instead. Type KERNEL at the REPL when ready to
load the PILL explicitly.

376/376 tests still passing.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: sigilante

src/forth.s

@@ -2846,7 +2846,7 @@ str_bench_def_end:
     .balign 8
     .global cold_start
 cold_start:
-    .quad   word_kernel
+    .quad   word_quit
 
 // ═════════════════════════════════════════════════════════════════════════════
 // ENTRY POINT