Repoint the TODO.md citations that no longer resolve

Its own SS0-SS9 structure survived the move to the tracker, so 133 citations
still resolve and are left alone. Thirteen did not.

Six named another repository's TODO.md by a section number: libakstdlib 1.6,
2.2.2 and 2.3, and libakgl's file. Those repositories dropped their numbering
entirely, so each now names UPGRADING.md, an issue, or the tracker.

Three cited 'TODO.md section 12', which has never existed here -- the defect
list is SS6. TODO.md itself caught two others of that class earlier. The
CMakeLists comment carried a stale premise with it: eleven defects
'deliberately reproduced and not yet fixed' stopped being the rule when SS0.1
retired the fidelity constraint.

Four told a reader to record work in TODO.md; the scanner defect is issue #4,
the audio_tables mutation gap is #25, and the UI gaps are libakgl #79 and #80.

Verified: cmake --build build && ctest --test-dir build, 112/112.

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

src/environment.c

@@ -172,7 +172,7 @@ akerr_ErrorContext *akbasic_environment_stop_waiting(akbasic_Environment *obj, c
 		     "NULL argument in stop_waiting");
     /*
      * The reference ignores `command` and clears unconditionally, which lets an
-     * inner block clear an outer block's wait (TODO.md section 12 item 3). The
+     * inner block clear an outer block's wait (TODO.md §6 item 3). The
      * argument is honoured here only to the extent of walking to the environment
      * that is actually waiting for it -- clearing the wrong one outright would
      * change observable control flow, so the search stops at the first match and