portability: replace M_PI / std::numbers::pi with a host+device-safe PI

M_PI is a POSIX <math.h> extension that MSVC does not define without
_USE_MATH_DEFINES. std::numbers::pi (introduced in the viewer guard commit) is
C++20, but CUDA here is compiled as C++17 (CMAKE_CUDA_STANDARD 17) and several
common/ headers are pulled into .cu device translation units, so std::numbers is
not available there.

Add common/JFJochMath.h with a dependency-free `constexpr double PI` that works
in host code (including MSVC), in CUDA device code, and under C++17/20, and use
it everywhere:
- common/ and image_analysis/ (incl. CUDA .cu): 78 M_PI occurrences, 22 files
- broker/OpenAPIConvert.cpp
- viewer/: the 5 files that used std::numbers::pi now use PI, for one consistent
  convention across the codebase

Verified to build: JFJochImageAnalysis (incl. CUDA), jfjoch_viewer, JFJochBroker.

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

viewer/image_viewer/JFJochAzIntImage.cpp

@@ -5,7 +5,7 @@
 #include <QVBoxLayout>
 
 #include "../../common/JFJochException.h"
-#include <numbers>
+#include "../../common/JFJochMath.h"
 
 JFJochAzIntImage::JFJochAzIntImage(QWidget *parent)
     : JFJochImage(parent) {
@@ -110,7 +110,7 @@ void JFJochAzIntImage::mouseDoubleClickEvent(QMouseEvent *event) {
         float phi = image->Dataset().az_int_bin_to_phi[idx];
 
         auto geom = image->Dataset().experiment.GetDiffractionGeometry();
-        auto coord = geom.ResPhiToPxl(2 * std::numbers::pi / q, phi / 180.0 * std::numbers::pi);
+        auto coord = geom.ResPhiToPxl(2 * PI / q, phi / 180.0 * PI);
         emit zoomOnBin(QPointF(coord.first, coord.second));
     }
 }