integration: carry the box-sum observed centroid through the profile path

Pass A (the box-sum) always computes an intensity-weighted centroid (the
observed spot position), but it was only emitted in BoxSum mode. Rotation
integration runs the profile path, so observed_x/y were left NAN there and no
positional (detector<->reciprocal) residual was possible downstream.

Emit the Pass-A centroid in the profile path too (CPU) and copy d_obs_x/d_obs_y
back in all modes (GPU) - Pass A fills them regardless of integrator mode.
observed_x/y are consumed only by the diagnostic HDF5 reflection table and the
viewer read-back; nothing in scaling/merge reads them, so merged output is
unchanged - the _process.h5 observed_x/y columns simply go from NAN to the real
centroid. This makes the observed position available to post-refinement.

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

image_analysis/bragg_integration/BraggIntegrationEngineCPU.cpp

@@ -345,8 +345,11 @@ std::vector<Reflection> BraggIntegrationEngineCPU::RunImpl(const Sampler &img,
             I = rh.I;
             sigma = rh.sigma;
         }
+        // Carry the Pass-A box-sum intensity-weighted centroid (observed spot position) through the
+        // profile path too - post-refinement uses it as the observed position (beam-centre / distance).
         results[i] = {static_cast<float>(I), static_cast<float>(sigma),
-                      static_cast<float>(rh.bkg), 0.0f, 0.0f, true, false};
+                      static_cast<float>(rh.bkg),
+                      static_cast<float>(rh.obs_x), static_cast<float>(rh.obs_y), true, rh.has_obs};
     }
 
     return Finalize(predicted, npredicted, results, image_number);