Fix WiX ICE80 mismatch: heat.exe never marked components as 64-bit

light.exe's ICE80 validation rejected essentially every harvested file
("This 32BitComponent ... uses 64BitDirectory") on the first build that
got far enough to reach it -- heat.exe's harvest command had no
-platform x64, so every component defaulted to 32-bit, while
product.wxs's own INSTALLFOLDER is correctly under
ProgramFiles64Folder (a 64-bit mingw64 toolchain is what's actually
being packaged). Real, on-disk mismatch, not a transient VM issue.

Also confirmed the earlier light.exe "timeout" wasn't a real bug either
-- a longer-budget retry finished linking fine in a few more minutes,
it was just slow, not hung.

Not yet re-verified against a live build (found right as this
session's VM time was already heavily spent) -- logged in TODO.md as
the next thing to confirm.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packaging/windows/oem/build.bat

@@ -49,7 +49,12 @@ REM here (see this file's top-of-file note).
 robocopy C:\msys64\mingw64 C:\build\dist\mingw64 /e /xd include share\doc share\man share\gtk-doc /nfl /ndl /njh /njs >> %LOG% 2>&1
 
 echo [build.bat] harvesting WiX components ... >> %LOG%
-C:\wix\heat.exe dir C:\build\dist -cg AppFiles -gg -scom -sreg -sfrag -srd -sw5150 -dr INSTALLFOLDER -var var.DistDir -out C:\build\files.wxs >> %LOG% 2>&1
+REM -platform x64: confirmed live (real light.exe run, not guessed) --
+REM without it heat.exe defaults every harvested component to 32-bit,
+REM which light.exe's ICE80 validation then rejects wholesale (~every
+REM single harvested file) once it's placed under INSTALLFOLDER, a
+REM 64-bit directory (this is a 64-bit mingw64 toolchain being packaged).
+C:\wix\heat.exe dir C:\build\dist -platform x64 -cg AppFiles -gg -scom -sreg -sfrag -srd -sw5150 -dr INSTALLFOLDER -var var.DistDir -out C:\build\files.wxs >> %LOG% 2>&1
 if errorlevel 1 (
   echo [build.bat] FAILED: heat.exe harvest failed >> %LOG%
   copy %LOG% Z:\build.log.failed >nul