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_convert.c

@@ -1,7 +1,7 @@
 /*
  * String -> number wrappers: aksl_atoi / atol / atoll / atof.
  *
- * TODO.md section 1.4, complete. The cases that used to live in
+ * Numeric conversion, complete. The cases that used to live in
  * tests/test_convert_strict.c -- registered as a known failure because the ato*
  * family had no error channel at all (2.1.5) -- are folded back in here now that
  * they pass: non-numeric input, empty input, trailing junk and overflow are all
@@ -95,7 +95,7 @@ static int test_trailing_junk_is_a_value_error(void)
 
 /*
  * "0x10" through the ato* forms is base 10, so parsing stops at the 'x' and the
- * rest is trailing junk. TODO.md 1.4 left this open; the answer is that the
+ * rest is trailing junk. The wrapper plan left this open; the answer is that the
  * prefix-honouring parse is aksl_strtol(nptr, NULL, 0, &dest), and tests/
  * test_strto.c holds that half.
  */
@@ -149,7 +149,7 @@ static int test_atoi_narrows_to_int_range(void)
     return 0;
 }
 
-/* TODO.md 1.4: the type boundaries round-trip exactly rather than nearly. */
+/* The type boundaries round-trip exactly rather than nearly. */
 static int test_type_boundaries_round_trip(void)
 {
     char buf[64];
@@ -229,7 +229,7 @@ static int test_atof_converts_and_rejects_null(void)
 }
 
 /*
- * TODO.md 1.4 left "inf" and "nan" open. They are accepted, because strtod(3)
+ * The wrapper plan left "inf" and "nan" open. They are accepted, because strtod(3)
  * accepts them and because they are exact round-trips rather than approximations
  * of something else -- a caller who did not want them has a domain check to make
  * that this library cannot make for it.