Correct the saturated-nucleus claim and cancel the booking it justified

The previous commit asserted that the 21 Jul Centaurus A data came back
with a saturated nucleus, and booked a short-exposure core set on T32 to
fix it. The assertion was wrong.

It came from taking the maximum pixel inside a 300 x 300 px box centred
on the frame. That measures the brightest thing near the middle of the
image, which is not the same as measuring the galaxy. The 65313 ADU
belonged to a foreground star 128 px (69 arcsec) from the nucleus, well
inside the box. Median filtering the inner 800 x 800 px to remove stars
leaves the galaxy peaking at 1944 ADU, roughly a thirtieth of the clip
level, with not one star-free pixel above 30000 ADU anywhere in that box.
The brightest pixel in the whole frame is at the right-hand edge, 2370 px
from centre.

The core looked blown in the processed image because of the stretch, not
the sensor: the white point sat at the 99.995th percentile, a level set
by field stars, so the galaxy's entire range from a 7 ADU sky to a 1944
ADU peak was compressed into the top few percent of the tone curve.
Re-rendering the same frames with a second curve scaled to the galaxy
recovered the core completely, with no new data.

The T32 reservation has been cancelled without running, so it cost
nothing. The other three reservations were verified intact afterwards
and quota is back to 6:05 of 8:00. plans/hdrcore-t32.txt stays in the
repo and on the scope: 47 Tuc and the SMC may genuinely saturate, a
dense cluster core being the fastest thing there is to clip, and the
ladder is ready if they do.

The corrected habit is recorded in CAMPAIGN.md: measure whether a core is
saturated before buying time to fix it, filtering stars out of the
measurement first. The check takes a minute and would have saved this
whole detour.

TODO.md also records a second result that affects future planning: the
faint outer halo of that stack is limited by the sky-plane subtraction,
which absorbed about 17.9 ADU/px of real halo light, rather than by
exposure time. More integration alone would not have gone deeper.

state/TODO.md

@@ -42,11 +42,24 @@
   two prior free reservations (749228, 749229) expired unused with reschedule=No;
   if 749314 also fails to run, stop rebooking and either walk it in (POST
   plan.asp per plans/README.md) or drop the free objective.
-- HDR core set on T32 runs 08:50-09:50 UTC 22 Jul (plans/hdrcore-t32.txt, ~25
-  pts). Verify after 09:50 UTC, then download and blend it under the saturated
-  core of the 21 Jul Cen A stack. The processing pipeline for that stack lives
-  in the user's Downloads\NGC5128\20260721\stacked\scripts folder, not in this
-  repo, with METHODS.md alongside it.
+- The T32 HDR core set (plans/hdrcore-t32.txt) was booked and then CANCELLED on
+  2026-07-21 without running: the Cen A nucleus is not saturated, the earlier
+  claim having measured a foreground star. See the correction in CAMPAIGN.md.
+  Zero points spent. The plan file remains available on T32 if a genuinely
+  saturated target turns up.
+- The 21 Jul Cen A data has been fully processed off-repo, in the user's
+  Downloads\NGC5128\20260721\stacked folder: masters, plate solution (0.27
+  arcsec on 237 stars), an LRGB composite, a globular cluster survey (289
+  candidates, 62% catalogue-confirmed, density falling 10.5x outward), surface
+  photometry (Sersic n = 4.27, Re = 400 arcsec, total G = 6.56, which matches
+  the catalogued brightness and so validates the photometric chain), and a
+  transient/moving-object search (both null, with measured limits). METHODS.md
+  there documents the lot. Nothing from that analysis needs to come back into
+  this repo, but two results affect FUTURE sessions and are recorded here:
+  **(a)** measure saturation properly before buying short subs, and **(b)** the
+  faint outer halo in that stack is limited by the sky-plane subtraction
+  (-17.9 ADU/px of real halo light absorbed), not by exposure time, so more
+  integration alone would not have gone deeper.
 - CrA on T8 runs 11:45-14:45 UTC 22 Jul. Verify after 14:45 UTC: images under
   /images/qisback/T8/ on t8.itelescope.net:8008, then the actual bill from
   account/history.aspx into the ledger. This is the first T8 bill, so it also