rugnux: use the project PI constant, not M_PI

MSVC does not define M_PI without _USE_MATH_DEFINES, and rugnux is part of
the portable subset that JFJOCH_VIEWER_ONLY builds. JFJochMath.h already
carries PI for exactly this reason.

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

rugnux/Rugnux.cpp

@@ -16,6 +16,7 @@
 #include <sstream>
 
 #include "../reader/JFJochHDF5Reader.h"
+#include "../common/JFJochMath.h"
 #include "../common/Logger.h"
 #include "../common/AzimuthalIntegrationMapping.h"
 #include "../common/AzimuthalIntegrationProfile.h"
@@ -400,7 +401,7 @@ namespace {
                 if (len < 1e-6 * lattice.Vec0().Length())
                     continue;
                 const double cosang = std::abs((axis * spindle) / (len * spindle_len));
-                const double ang = std::acos(std::min(1.0, cosang)) * 180.0 / M_PI;
+                const double ang = std::acos(std::min(1.0, cosang)) * 180.0 / PI;
                 if (!best.has_value() || ang < best->first)
                     best = std::make_pair(ang, order);
                 break;