Drop the TODO.md section numbers from 26 files

Eighty-five comments cited section numbers -- 1.1, 2.2.6, 3.6 -- from a
numbering the file had already abandoned before the move to the tracker. They
label completed work, so the pointer was the only wrong part.

The citation is removed and the sentence kept, which is what issue #27
recommended: these are labels, not references, and a label carrying a
version-dependent pointer goes stale again at the next reorganisation. Where a
pointer earns its place it names what actually holds the content now --
UPGRADING.md for the confirmed defects, libakerror #15 for the target
namespacing, issue #7 for the mutation survivors.

README.md and akstdlib.h sent readers to TODO.md for 'what is still open';
they name the tracker.

Verified: cmake --build build && ctest --test-dir build, 19/19.

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

tests/test_linkedlist.c

@@ -1,5 +1,5 @@
 /*
- * Linked list -- TODO.md section 1.7, complete.
+ * Linked list.
  *
  * The two confirmed list defects are fixed, so the tests that used to live in
  * tests/test_list_append_chain.c and tests/test_list_iterate_head.c are folded
@@ -59,7 +59,7 @@ static akerr_ErrorContext AKERR_NOIGNORE *record_visit(aksl_ListNode *node, void
 /* ---------------------------------------------------------------------- */
 
 /*
- * TODO.md 2.2.14: every caller used to have to remember to memset a node before
+ * every caller used to have to remember to memset a node before
  * its first use, and a stack node that skipped it walked straight into garbage.
  */
 static int test_node_init_zeroes_the_links(void)
@@ -103,7 +103,7 @@ static int test_append_single_node(void)
  * The defect that made this library's list unusable: `tail` was assigned from
  * Floyd's `slow` cursor *before* slow advanced, so it tracked the node behind
  * the midpoint rather than the last node. Appending n1..n4 to n0 produced the
- * chain "n0 -> n4" and silently dropped n1, n2 and n3. TODO.md 2.1.1.
+ * chain "n0 -> n4" and silently dropped n1, n2 and n3.
  */
 static int test_append_builds_the_whole_chain(void)
 {
@@ -218,7 +218,7 @@ static int test_append_detects_cycle_below_the_head(void)
 }
 
 /*
- * TODO.md 1.7 asked for the aliasing contract to be defined. It is refusal:
+ * The wrapper plan asked for the aliasing contract to be defined. It is refusal:
  * relinking a node that is already in the list would orphan everything between
  * its old position and the tail, so the tail walk -- which happens anyway --
  * doubles as the check.
@@ -281,7 +281,7 @@ static int test_iterate_single_node(void)
  * Every node, exactly once, in order, starting at the head. The cycle check
  * leaves Floyd's `slow` cursor at the list midpoint, and the visiting loop used
  * to start from there -- so the whole first half of the list, head included, was
- * never passed to the callback at all. TODO.md 2.1.2.
+ * never passed to the callback at all.
  */
 static int test_iterate_visits_every_node_from_the_head(void)
 {
@@ -470,7 +470,7 @@ static int test_pop_middle_node(void)
 }
 
 /*
- * TODO.md 2.2.12: popping the head used to leave the caller's own head pointer
+ * popping the head used to leave the caller's own head pointer
  * aimed at a node that was no longer in the list, with no way to learn the new
  * one. That is what the head out-param is for, and this is the assertion.
  */
@@ -572,7 +572,7 @@ static int test_pop_then_iterate(void)
 }
 
 /*
- * TODO.md 1.7's pool-accounting case. AKSL_RUN already asserts that each test
+ * The wrapper plan's pool-accounting case. AKSL_RUN already asserts that each test
  * leaves the pool as it found it; this one drives enough failures in a row to
  * exhaust the pool several times over, which is where a wrapper that raises an
  * error and forgets to release it shows up as an outright exhaustion rather than