Fix FFTW build-tree header wiring and two MSVC warnings

FFTW exposes fftw3.h only via $<INSTALL_INTERFACE:include>, so consuming
fftw3f from the build tree (FetchContent) leaves FFTIndexerCPU.h unable to
find the header. A system-installed fftw3.h masks this on Linux, so it only
bit on Windows; add the source-tree api/ dir to fftw3f's interface includes.

Also two viewer-reachable warnings:
- time_utc.h (C4477): %03ld was fed a chrono milliseconds::rep (64-bit), not
  a long; cast the 0-999 value to int and use %03d.
- HDF5Objects.h (C4700): value-initialize the scalar read buffer.

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

CMakeLists.txt

@@ -207,6 +207,10 @@ FetchContent_Declare(fftw
         URL_HASH SHA256=56c932549852cddcfafdab3820b0200c7742675be92179e59e6215b340e26467
         EXCLUDE_FROM_ALL)
 FetchContent_MakeAvailable(fftw)
+# FFTW exposes fftw3.h only via $<INSTALL_INTERFACE:include>, so consuming fftw3f straight from
+# the build tree (FetchContent) leaves the header unreachable. On Linux a system-installed
+# fftw3.h masks this; on Windows it does not. Add the source-tree api/ dir for build-tree use.
+TARGET_INCLUDE_DIRECTORIES(fftw3f INTERFACE $<BUILD_INTERFACE:${fftw_SOURCE_DIR}/api>)
 ADD_COMPILE_DEFINITIONS(JFJOCH_USE_FFTW)
 
 IF (JFJOCH_VIEWER_ONLY)

common/time_utc.h

@@ -27,7 +27,7 @@ inline std::string time_UTC(const std::chrono::time_point<std::chrono::system_cl
         throw std::runtime_error("gmtime failed");
 
     strftime(buf1, sizeof(buf1), "%FT%T", &tm_utc);
-    snprintf(buf2, sizeof(buf2), ".%03ld", time_ms % 1000);
+    snprintf(buf2, sizeof(buf2), ".%03d", static_cast<int>(time_ms % 1000));
     return std::string(buf1) + std::string(buf2) + "Z";
 }
 

writer/HDF5Objects.h

@@ -264,7 +264,7 @@ public:
         if (file_space.GetNumOfDimensions() != 0)
             throw JFJochException(JFJochExceptionCategory::HDF5, "Dataset tries to read scalar from vector dataset");;
 
-        T output;
+        T output{};
         if (H5Dread(id, HDF5DataType(output).GetID(), mem_space.GetID(), H5S_ALL, H5P_DEFAULT, &output) < 0)
             throw JFJochException(JFJochExceptionCategory::HDF5, dataset_name + ": read unsuccessful");
         return output;