Produce the four deliverable images and the science outputs for every session

The four-image set worked out on Centaurus A is now generated for any
target, because its value is the comparison: the same data at four levels
of treatment, so a viewer can see what processing did and did not add.
colour.py's assembly is driven by flags - gradient, neutralise, denoise,
saturation, hdr, protect-compact - so the baseline and the fully
corrected version come from ONE code path and the only differences
between them are the ones named.

Image 3 applies what the measurements justify rather than a house style.
Each item is there because measuring the first session caught the
conventional version getting something wrong: a plane fit that had
absorbed 17.9 ADU/px of galaxy halo, a core flattened by a white point
set by field stars, deconvolution ringing around every bright star, and
denoising erasing faint compact sources that turned out to be globular
clusters. Compact sources are now explicitly protected from smoothing -
2374 of them on NGC 2030.

The close-up revealed a real design error, caught by its own assertion.
Forcing a square crop cannot contain a target wider than the frame is
tall, which is the normal case for a nebula in a wide field, and the
assertion fired rather than silently cutting the subject in half. Crops
are no longer square, and when a target genuinely fills the field the
close-up is skipped with that said plainly - re-saving image 3 under a
name claiming to be a close-up would be worse than producing nothing.

science.py adds the measurements that generalise to any target:
photometric calibration from the field's own Gaia stars, the limiting
magnitude actually reached, a source catalogue with calibrated
magnitudes, an annotated field placed by the plate solution, and a radial
surface-brightness profile. Object-specific analyses stay hand-driven,
because a cluster survey suits a galaxy and is meaningless for a nebula.

All of it depends on astrometry, so an unsolved session gets no science
and says so instead of quietly producing less. NGC 2030 calibrates to a
zero point of 24.794 with 0.202 mag scatter on 917 stars, 3470 sources,
limiting G of 18.2.

pipeline/run.py

@@ -21,7 +21,8 @@ import traceback
 import layout
 import session as session_mod
 
-STAGES = ("ingest", "measure", "register", "solve", "colour", "report")
+STAGES = ("ingest", "measure", "register", "solve", "colour",
+          "science", "report")
 
 
 def _exists(path):
@@ -89,6 +90,17 @@ def process(root, stages=STAGES, force=False, verbose=True):
             print("    colour")
             results["final"] = colour.run(s, verbose=verbose)
 
+        if "science" in stages:
+            import science
+            print("    science")
+            try:
+                results["science"] = science.run(s, verbose=verbose)
+            except Exception as exc:                          # noqa: BLE001
+                # Measurements are a bonus on top of the images; losing them
+                # must not lose the pictures too.
+                print(f"      science failed: {type(exc).__name__}: {exc}")
+                results["science"] = None
+
         if "report" in stages:
             import report
             print("    report")