Azimuthal integration: optional sigma clipping of the reported profile

The profile is the MEAN of each bin, so a few strong reflections landing in a bin
lift it exactly as a smooth powder ring does. That is the wrong quantity whenever
the profile is wanted as a background rather than as a measurement of what is in
the bin - the ice score being the case in point, where reading a plain profile
INVERTED the metric: over 37 rotation crystals the two highest-scoring crystals
had no ice at all.

The adaptive spot finder already computes the right thing, a sigma-clipped
per-resolution-ring background, as a byproduct of its own threshold. Where it
runs, the ice score uses that. Where it does not - --no-adaptive-spots,
--azint-only, and anything reading the profile the broker wrote - there was no way
to get it. This adds one: azim_int_settings.sigma_clip (rugnux --azim-sigma-clip),
0 = off, minimum 2 because a tighter clip rejects a large part of a clean Gaussian
bin and biases the estimate low rather than removing outliers.

Two clip passes follow the plain one, matching the finder's recipe - the first
pass's standard deviation is itself inflated by the peaks being removed, so one
pass leaves a threshold that is still too generous. A bin with fewer than eight
pixels is left alone: at the detector edge and behind the beam stop there is no
spread to clip on.

Both engines do it. On the GPU the accept range is computed by a small kernel and
stays resident, so a clip pass is one more read of the same pixels and no round
trip; the two accumulation kernels take the range as a pointer that is null on the
plain pass. Measured on a JUNGFRAU rotation dataset, non-adaptive path: azimuthal
integration 0.02 -> 0.06 ms per image, exactly the 3x the extra passes predict,
against a 0.34 ms per-image total.

Note what the result IS: the smooth background under the peaks, not the bin mean.
It should not be switched on where a ring's integrated intensity is wanted - the
powder-ring geometry fit reads ring peaks, and those are what a clip is designed
to remove. Off by default, so nothing changes unless it is asked for.

Not exposed over the REST API - that needs the generated model regenerated, which
is a separate step.

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

common/ScalingSettings.cpp

@@ -164,15 +164,6 @@ bool ScalingSettings::GetExpectedVarianceMerge() const {
     return expected_variance_merge;
 }
 
-ScalingSettings &ScalingSettings::IceRingMergeMask(bool input) {
-    ice_ring_merge_mask = input;
-    return *this;
-}
-
-bool ScalingSettings::GetIceRingMergeMask() const {
-    return ice_ring_merge_mask;
-}
-
 float ScalingSettings::GetIceMinScore() const {
     return ice_min_score;
 }