migrate pyqt5 to pyside6

build/studio/constraints-build.txt

@@ -4,7 +4,11 @@
 # on the spec (which Qt, which numpy, which hooks-contrib), so a build that "works" on one
 # machine and produces a non-starting EXE on another is usually a version difference that
 # nobody wrote down. `-c` constrains whatever else asks for these packages, so the app's
-# own loose requirements (PyQt5>=5.15, scipy>=1.10.1, ...) resolve to exactly this set.
+# own loose requirements (PySide6>=6.6, scipy>=1.10.1, ...) resolve to exactly this set.
+#
+# PySide6 rather than PyQt5: the apps are LGPLv3-bound. PyQt5 must not be present in the
+# build environment at all — `pyqtgraph` binds to whichever toolkit it finds first, so a
+# leftover PyQt5 produces plots built from the wrong binding (setup.ps1 uninstalls it).
 #
 # `orisys` is deliberately absent: it is installed from a local checkout (or deliberately
 # from PyPI with -FromPypi), and pinning it by name would fight the editable install.
@@ -15,9 +19,10 @@
 PyInstaller==6.22.2
 pyinstaller-hooks-contrib==2026.7
 PyOpenGL==3.1.10
-PyQt5==5.15.11
-PyQt5-Qt5==5.15.2
-PyQt5-sip==12.19.0
+PySide6==6.11.2
+PySide6-Essentials==6.11.2
+PySide6-Addons==6.11.2
+shiboken6==6.11.2
 numpy==2.2.6
 scipy==1.15.3
 numba==0.67.0