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_tree.c

@@ -1,5 +1,5 @@
 /*
- * Tree traversal -- TODO.md section 1.8, complete.
+ * Tree traversal.
  *
  * The old version of this file counted steps, which cannot tell the three
  * depth-first orders apart because all three visit all seven nodes -- and could
@@ -183,7 +183,7 @@ static int test_dfs_is_an_alias_for_preorder(void)
 
 /*
  * BFS was AKERR_NOT_IMPLEMENTED, and the lalloc/lfree parameters that existed to
- * serve it were defaulted and then never called -- TODO.md 2.2.8 and 2.2.10.
+ * serve it were defaulted and then never called. See UPGRADING.md.
  * Both modes work now, and the allocator test below proves the queue is real.
  */
 static int test_bfs_visits_level_by_level(void)
@@ -249,7 +249,7 @@ static akerr_ErrorContext AKERR_NOIGNORE *counting_free(void *ptr)
 }
 
 /*
- * TODO.md 1.8: "Custom lalloc/lfree are actually invoked -- currently they are
+ * The wrapper plan asked that "custom lalloc/lfree are actually invoked -- currently they are
  * stored and never called". They are called now, once per node enqueued, and
  * every allocation is released. The depth-first modes allocate nothing at all,
  * which is the other half of the contract.
@@ -382,7 +382,7 @@ static int test_degenerate_chains(void)
 }
 
 /*
- * TODO.md 1.8 / 2.2.7: a chain deeper than the recursion can take. It used to
+ * A chain deeper than the recursion can take. It used to
  * overflow the stack; it is AKERR_OUTOFBOUNDS now, and the message names the
  * documented limit. Built one node past the cap so the failure is the cap itself
  * and not some incidental shortfall. `static` because AKSL_TREE_MAX_DEPTH nodes
@@ -488,7 +488,7 @@ static int test_cyclic_tree_is_caught(void)
  * that raised the break handled it in its own PROCESS/HANDLE block and returned
  * success, so the parent frame's PASS saw nothing wrong and carried straight on
  * into the sibling subtree. All seven nodes were visited no matter where the
- * break was raised. TODO.md 2.1.3.
+ * break was raised.
  *
  * One case per order, each breaking on a node that is *not* last in that order --
  * which is precisely what the old test could not do, because it hid its target
@@ -579,7 +579,7 @@ static int test_null_arguments(void)
 }
 
 /*
- * TODO.md 2.2.9: the switch had no default, so an unrecognised mode -- and
+ * the switch had no default, so an unrecognised mode -- and
  * AKSL_TREE_SEARCH_VISIT, which the header documented but nothing implemented --
  * fell straight through to SUCCEED_RETURN having visited nothing at all. A
  * traversal that silently did not happen, reported as success.