docs: archive the frozen stage code as one compressed tarball

docs/history kept six stages with a full copy of the project under code/,
3.8 mb of sources duplicated from stage to stage and already superseded. store
them as docs/history/code-snapshots.tar.gz, 0.66 mb, and extract one in place
to read it. every stage's notes.md stays browsable, and the index says where the
code went and how to get it back.

the top-level README points at the archive too. its other two links into
docs/history, 21-micro and 35-bench, were notes that were never kept and do not
resolve; the index now records that.

1 files changed, 0 insertions, 6 deletions

diff --git a/docs/history/17-o3-boundaries/code/io_linux.c b/docs/history/17-o3-boundaries/code/io_linux.c
deleted file mode 100644
index 7ea34e0..0000000
--- a/docs/history/17-o3-boundaries/code/io_linux.c
+++ /dev/null
@@ -1,6 +0,0 @@
-#include <stdio.h>
-int J;
-static int pk(void){int c=getchar();ungetc(c,stdin);return c==EOF;}
-char Q(void){int c=getchar();J=pk();return c;}
-void G(char c){putchar(c);}
-__attribute__((constructor)) static void init(void){J=pk();}