PixelRefine: env-gated orientation + cell-scale sweep (PR_SWEEP) for R-free A/B

R-free validation (full jet, 1.5 A) confirmed the r1_multiplier fix: PR x6 beats
traditional (R-free 0.2625 vs 0.2802), the multiplier optimum is ~6 (x6==x9 on
R-free; x9 only buys CC1/2 internal consistency), and per-image orientation
*refinement* is a no-op (0.2618 vs 0.2625).

Re-adds the reference-driven orientation + uniform cell-scale SWEEP behind PR_SWEEP
(off by default) to test whether the cell-scale degree of freedom - which the
gradient orientation refinement lacks, and which moves the high-res shells radially
- helps R-free at 1.5 A on serial data. CCref is a near-no-op on the jet (as for
the gradient path), but that does not certify R-free, so it is left for validation.

NOTE: PR_RMULT / PR_ORIENT / PR_SWEEP remain temporary diagnostic env knobs; once
the sweep R-free is in, bake r1_multiplier=6, drop the no-op paths, strip the knobs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

image_analysis/IndexAndRefine.cpp

@@ -450,6 +450,7 @@ bool IndexAndRefine::PixelRefineIntegrate(DataMessage &msg,
     prd.shoebox_radius = static_cast<int>(std::lround(experiment.GetBraggIntegrationSettings().GetR1()));
     if (const char *m = std::getenv("PR_RMULT")) prd.r1_multiplier = std::stod(m); // TEMP: Term-2 R1 multiplier sweep
     if (std::getenv("PR_ORIENT")) prd.refine_orientation = true; // A/B: per-image orientation refinement
+    if (std::getenv("PR_SWEEP")) prd.sweep_orientation = true; // A/B: orientation + cell-scale sweep
 
     std::vector<uint8_t> buffer;
     const uint8_t *ptr = image.GetUncompressedPtr(buffer);