Keep the defect list in TODO.md and point PERFORMANCE.md at it

The six defects the perf suites turned up were written out in full in both
files. TODO.md is where a defect belongs -- file, line, functional
consequence, blast radius, what closing it touches -- and duplicating that
in a report guarantees the two drift, with no way to tell which copy is
current.

PERFORMANCE.md keeps what is actually its argument: that stress testing
reaches failures a suite calling each function a handful of times does not,
and that two of the six kill the process rather than slowing it down. The
detail is one reference away.

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

README.md

@@ -387,4 +387,4 @@ AKGL_BENCH_SCALE=0.1 ctest --test-dir build -L perf  # a tenth of the iterations
 
 Each measurement is the best of five runs and is held to a budget set at roughly ten times the recorded baseline, so a suite that turns red means an algorithmic regression rather than a busy machine. Budgets are enforced only in an optimized build at full scale; below `AKGL_BENCH_SCALE=1.0`, and in a coverage build, they are reported without failing.
 
-`PERFORMANCE.md` carries the recorded baseline, the frame budget it adds up to, and what the numbers say — including the raw-SDL control rows that separate what libakgl costs from what the rasterizer costs, and the six defects the stress tests turned up.
+`PERFORMANCE.md` carries the recorded baseline, the frame budget it adds up to, and what the numbers say — including the raw-SDL control rows that separate what libakgl costs from what the rasterizer costs. The six defects the stress tests turned up, and the targets the numbers are measured against, are in `TODO.md` under **Performance**.