Reindent to the canonical stroustrup style

Whitespace only -- `git diff -w` is empty. TODO.md 2.3 recorded that the
tree mixed hard tabs and space indents within the same functions;
tests/aksl_capture.h was the worst of it, with the assertion macros
space-indented and everything around them tabbed.

The style is the one libakerror standardised on and the one AGENTS.md
already describes: Emacs cc-mode "stroustrup", c-basic-offset 4,
indent-tabs-mode on, tab-width 8. A correct file is a fixed point of
indent-region under those settings, and the tree is one now -- a second
pass produces no diff.

scripts/reindent.el is that pass, checked in so "correct" is something
you can run rather than something you have to remember. It is not
clang-format and deliberately so: AGENTS.md forbids introducing one
without discussion, and this is a good illustration of why. cc-mode
indents every declaration in akstdlib.h one level for the extern "C" { }
wrapping the file body, so the script sets inextern-lang to 0 -- a
cc-mode offset with no clang-format equivalent, and without it the first
run moved 364 lines in the wrong direction.

Its own commit, no behaviour change, and the suite is green either side.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/collections.c

@@ -106,8 +106,8 @@ akerr_ErrorContext AKERR_NOIGNORE *aksl_list_insert_after(aksl_ListNode *node, a
  * the case a caller is most likely to get wrong by hand.
  */
 akerr_ErrorContext AKERR_NOIGNORE *aksl_list_insert_before(aksl_ListNode **head,
-							  aksl_ListNode *node,
-							  aksl_ListNode *obj)
+							   aksl_ListNode *node,
+							   aksl_ListNode *obj)
 {
     PREPARE_ERROR(e);
     FAIL_ZERO_RETURN(e, head, AKERR_NULLPOINTER, "head=%p, node=%p, obj=%p",