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>

CMakeLists.txt

@@ -78,7 +78,7 @@ endif()
 # Sanitizer build, off by default:
 #   cmake -S . -B build-asan -DAKSL_SANITIZE=ON && ctest --test-dir build-asan
 # Set before the dependency is added so libakerror is instrumented too --
-# several of the defects in TODO.md section 2 (the uninitialised %s in
+# several of the defects listed in UPGRADING.md (the uninitialised %s in
 # aksl_realpath, the unbounded vsprintf in aksl_sprintf, the missing va_end in
 # the printf family) only show up under ASan/UBSan.
 option(AKSL_SANITIZE "Build the library and its tests with ASan + UBSan" OFF)
@@ -298,7 +298,7 @@ install(FILES
 #                             reaching FINISH_NORETURN, a deliberate contract
 #                             violation), so a non-zero exit is a pass.
 #   AKSL_KNOWN_FAILING_TESTS  assert the *correct* behaviour of a confirmed
-#                             defect from TODO.md section 2.1. They fail until
+#                             defect; see UPGRADING.md. They fail until
 #                             the defect is fixed, and are marked WILL_FAIL so
 #                             the suite stays green and the gap stays visible.
 #                             When one is fixed CTest reports it as failed with