windows: bundle cuFFT in installer and tag the CUDA/CPU variant

cuFFT is the only CUDA component linked dynamically (cudart and the
fast-feedback indexer are static), so the prior Windows installer would
fail to launch the GPU path on a host without a CUDA toolkit. Ship
cufft64_*.dll next to the viewer (CUDA 13 keeps it in bin/x64, earlier
toolkits in bin); the DLL is self-contained, so the installed app needs
only an NVIDIA driver.

Tag the variant where it matters and nowhere else: the installer
filename (-cuda<major> / -cpu) and the Add/Remove Programs entry
("Jungfraujoch (CUDA)" / "(CPU)") advertise it, while the install folder
and Start Menu group stay plain "Jungfraujoch" -- the CUDA build is a
strict superset, so the two variants share a location and replace each
other.

Docs: SOFTWARE.md + JFJOCH_VIEWER.md.

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

CMakeLists.txt

@@ -361,11 +361,26 @@ elseif (WIN32)
     # GPLv3 text shown as the click-through license page of the installer.
     set(CPACK_RESOURCE_FILE_LICENSE "${CMAKE_SOURCE_DIR}/LICENSE")
 
-    # Name the install folder and Start Menu group "Jungfraujoch". CPack uses this single
-    # variable for both; without it they default to "jfjoch <version>".
+    # Branding is split across three CPack knobs so the CUDA/CPU variant surfaces exactly where we
+    # want it and nowhere else:
+    #   - Install folder + Start Menu group come from CPACK_PACKAGE_INSTALL_DIRECTORY and
+    #     CPACK_NSIS_PACKAGE_NAME (the latter feeds $(^Name), the Start Menu group's default folder).
+    #     Both stay plain "Jungfraujoch", so the Start Menu group carries no variant tag and the two
+    #     builds install to the same place (CUDA is a strict superset -- they replace, not coexist).
+    #   - CPACK_NSIS_DISPLAY_NAME is the Add/Remove Programs entry -- tagged "(CUDA)"/"(CPU)".
+    #   - CPACK_PACKAGE_FILE_NAME is the installer .exe filename -- tagged "-cuda<major>"/"-cpu", so
+    #     the (much larger) CUDA download is self-identifying, with the CUDA major version baked in.
+    # The tag follows JFJOCH_CUDA_AVAILABLE automatically; CUDAToolkit_VERSION_MAJOR is set whenever
+    # it is ON (find_package(CUDAToolkit) ran in the same guard above).
     set(CPACK_PACKAGE_INSTALL_DIRECTORY "Jungfraujoch")
-    set(CPACK_NSIS_DISPLAY_NAME "Jungfraujoch")
     set(CPACK_NSIS_PACKAGE_NAME "Jungfraujoch")
+    if (JFJOCH_CUDA_AVAILABLE)
+        set(CPACK_NSIS_DISPLAY_NAME "Jungfraujoch (CUDA)")
+        set(CPACK_PACKAGE_FILE_NAME "jfjoch-${JFJOCH_VERSION}-win64-cuda${CUDAToolkit_VERSION_MAJOR}")
+    else()
+        set(CPACK_NSIS_DISPLAY_NAME "Jungfraujoch (CPU)")
+        set(CPACK_PACKAGE_FILE_NAME "jfjoch-${JFJOCH_VERSION}-win64-cpu")
+    endif()
 
     # Start Menu shortcut for the viewer ("<exe basename>;<label>"). The shortcut and the
     # Add/Remove Programs entry both use the .exe's embedded icon.

docs/JFJOCH_VIEWER.md

@@ -106,13 +106,24 @@ Notes:
 - For a machine without an NVIDIA GPU, add `-DJFJOCH_USE_CUDA=OFF`: the viewer then runs the same
   pipeline on the CPU (FFTW indexer) at lower throughput.
 
-To produce a self-contained installer (bundles the Qt runtime via `windeployqt` and the analysis
-CLIs), with NSIS installed:
+To produce a self-contained installer (bundles the Qt runtime via `windeployqt`, the analysis CLIs,
+and — on the CUDA build — the cuFFT runtime DLL, so the target host needs no Qt and no CUDA toolkit,
+only an NVIDIA GPU driver), with NSIS installed:
 
 ```
 cd build-win
 cpack
 ```
 
-The NSIS generator is selected automatically on Windows (no `-G` needed); this writes
-`jfjoch-<version>-win64.exe`.
+The NSIS generator is selected automatically on Windows (no `-G` needed). The installer filename and
+the Add/Remove Programs entry mark the CUDA/CPU variant, while the install folder and Start Menu
+group stay plain `Jungfraujoch` (the two variants share an install location and replace each other —
+CUDA is a strict superset):
+
+| Build | Installer file | Add/Remove Programs |
+| --- | --- | --- |
+| CUDA (default) | `jfjoch-<version>-win64-cuda<major>.exe` | `Jungfraujoch (CUDA)` |
+| `-DJFJOCH_USE_CUDA=OFF` | `jfjoch-<version>-win64-cpu.exe` | `Jungfraujoch (CPU)` |
+
+`<major>` is the CUDA toolkit major version (e.g. `cuda13`). The cuFFT DLL is ~256 MB, so the CUDA
+installer is correspondingly larger — hence the variant tag in the filename.

docs/SOFTWARE.md

@@ -10,7 +10,9 @@ but likely possible with providing some packages from external repositories.
 The desktop viewer `jfjoch_viewer` (only) can additionally be built on **Windows 11** with Visual
 Studio 2026 (MSVC), CUDA 13.3 and Qt 6.11 — see
 [jfjoch_viewer ▸ Building from source on Windows](JFJOCH_VIEWER.md#building-from-source-on-windows).
-The rest of Jungfraujoch is Linux-only.
+The Windows installer bundles the Qt runtime, and on the CUDA build the CUDA runtime (cuFFT) as
+well, so end users need neither Qt nor a CUDA toolkit installed — only an NVIDIA GPU driver for the
+GPU path. The rest of Jungfraujoch is Linux-only.
 
 
 ## Software dependencies

viewer/CMakeLists.txt

@@ -168,3 +168,18 @@ IF(Qt6_VERSION VERSION_GREATER_EQUAL "6.5")
             NO_UNSUPPORTED_PLATFORM_ERROR)
     INSTALL(SCRIPT ${jfjoch_viewer_deploy_script} COMPONENT viewer)
 ENDIF()
+
+# Bundle the cuFFT runtime DLL next to the viewer so the installed app runs on Windows hosts that
+# have an NVIDIA driver but no CUDA toolkit. cuFFT is the ONLY CUDA component we link dynamically
+# (cudart and the fast-feedback indexer are static), so it is the one runtime file the toolkit would
+# otherwise have to provide; the DLL is self-contained (depends only on KERNEL32). CUDA 13 keeps
+# redistributable DLLs in bin/x64, earlier toolkits in bin -- glob both. Windows + GPU build only.
+IF(WIN32 AND JFJOCH_CUDA_AVAILABLE)
+    FILE(GLOB _cufft_dll
+            "${CUDAToolkit_BIN_DIR}/x64/cufft64_*.dll"
+            "${CUDAToolkit_BIN_DIR}/cufft64_*.dll")
+    IF(NOT _cufft_dll)
+        MESSAGE(FATAL_ERROR "cuFFT runtime DLL not found under ${CUDAToolkit_BIN_DIR}")
+    ENDIF()
+    INSTALL(FILES ${_cufft_dll} DESTINATION bin COMPONENT viewer)
+ENDIF()