Move outstanding work from TODO.md into the issue tracker

Twenty-six issues on source.starfort.tech/andrew/libakstdlib, labelled by kind
and blast radius and milestoned by what they can land in: 0.2.x for anything
that breaks no ABI, 0.3.0 for new public symbols, 1.0.0 for the large surfaces.
Everything filed carries status::grooming.

The four items blocked on libakerror are filed in both places -- the fix is
there and the bill is here -- and TODO.md keeps a table saying which is which.

What stays in TODO.md is what a tracker has no place for: where the library
stands, why six libc functions are deliberately not wrapped, which eight
uncovered lines are uncoverable rather than untested, and the akbasic call
counts that prioritised everything built since. 377 lines to 189.

Filed alongside: 25 file headers in tests/ and src/ cite TODO.md section
numbers from a numbering the file itself had already abandoned. They label
completed work, so nothing about the code is misleading -- only the pointer is.
Left for its own commit rather than churning 25 files here.

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

UPGRADING.md

@@ -10,7 +10,7 @@ this up. Rebuild against the new header.
 `AKSL_VERSION_CHECK()` catches the pairing at runtime if a stale `.so` ever does
 end up on the path.
 
-Everything below comes out of `TODO.md` sections 2.1 and 2.2 — the confirmed
+Everything below was recorded in `TODO.md` before the move to the tracker — the confirmed
 defects, all of which were reproduced against the 0.1.0 library before being
 fixed.