rugnux: remove the beam-centre ladder (--beam-center-search)

The ladder stepped the beam centre a pixel at a time after a rotation first pass that indexed fewer
than half the validation frames. A battery with it switched off changed no output, so it goes: the
option, its usage text, ProcessConfig::beam_center_search_pxl, the once-per-run flag that kept
probes, walks and later passes from re-running it, and the docs. The background centre
measurement, the beam-centre check that indexes at the measured centre, the merge-judged arms and
the post-refinement of the centre are unchanged. rugnux now rejects --beam-center-search as an
unknown option.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SVmAWnzCmRKAXVUCdc4iNi

image_analysis/IndexAndRefine.cpp

@@ -162,9 +162,9 @@ IndexAndRefine::IndexingOutcome IndexAndRefine::DetermineLatticeAndSymmetry(Data
     const bool index_ice_rings = experiment.GetIndexingSettings().GetIndexIceRings();
     // Read per call, for the same reason: a beam-centre hypothesis moves the geometry after this
     // object is built, and a spot mapped into reciprocal space through the centre the run started at
-    // is not the spot the trial centre sees. Held at construction, this scored every hypothesis of the
-    // beam-centre ladder against the file's geometry - which is why a centre scored 42/60 inside the
-    // ladder and 5/60 when the same value was given on the command line.
+    // is not the spot the trial centre sees. Held at construction, this scored every beam-centre
+    // hypothesis against the file's geometry - which is why a centre once scored 42/60 as a trial and
+    // 5/60 when the same value was given on the command line.
     const DiffractionGeometry geom = experiment.GetDiffractionGeometry();
     for (size_t seed_cap : {size_t{30}, size_t{80}, std::numeric_limits<size_t>::max()}) {
         std::vector<Coord> recip;