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>

TODO.md

@@ -2331,7 +2331,7 @@ gitignored is exactly what makes it invisible. **Keep build trees out of the sou
 and if a coverage number looks suspiciously unchanged, `find . -name '*.gcda'` before believing
 it.
 
-Branch coverage reads 18.0% and is not a target, for the reason `libakgl/TODO.md` and
+Branch coverage reads 18.0% and is not a target, for the reason `libakgl` and
 `libakstdlib` both give: the akerror control-flow macros expand into large branch trees
 at every call site, most of them unreachable in normal operation. Track line and function
 coverage.