feat(admission): teach the wired-limit lever in every rejection

Admission rejections surface verbatim in the app's error chip, and the
ceiling they fire against is often raisable: measured live, dots3-note
was rejected at 20k context against the 107.52GB macOS default on a
128GB Mac that serves the same work at 120GB. All three rejection sites
(per-chunk valve, hybrid chunk valve, whole-span check) now append an
advisory naming iogpu.wired_limit_mb and the sudo sysctl invocation,
with the cautions that matter: leave at least 8GB for macOS or the
system may become unstable, and the setting resets on reboot.