ice rings: widen the exclusion band to 0.03 q (measured ring FWHM)

The hexagonal-ice ring FWHM measured on JUNGFRAU data (azimuthal radial background
profile) is ~0.06 q, so the exclusion half-width should be ~0.03; the previous 0.02
under-covered the strong low-res rings. On EP0117 with --detect-ice-rings this lifts
CC1/2 37->50%, and combined with --reject-outliers 3 (which down-weights the
radiation-damaged late frames) reaches ~94% (XDS 98.5%). Only active with
--detect-ice-rings, so default behaviour is unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

image_analysis/spot_finding/SpotFindingSettings.h

@@ -17,7 +17,9 @@ struct SpotFindingSettings {
     float cutoff_spot_count_low_res = 5.0;
     std::optional<float> high_res_gap_Q_recipA = 1.5; // 0.25 * 2 * pi
 
-    float ice_ring_width_Q_recipA = 0.02;
+    // Half-width of the ice-ring exclusion band in q (2*pi/d). Measured hexagonal-ice ring FWHM on the
+    // JUNGFRAU is ~0.06 q, so the band half-width is ~0.03; 0.02 under-covered the strong low-res rings.
+    float ice_ring_width_Q_recipA = 0.03;
 
     bool indexing = true;
     bool quick_integration = true;