Previous BAT script falsely reported success because `if exist` checked
the pre-existing file, not the copy result. Now: deletes old DST first,
copies with /B (binary), verifies size matches expected, logs all errors.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
VBS→PowerShell chain was silently failing. BAT is simpler, doesn't depend
on execution policy, and writes detailed log to %TEMP%\sm_update.log
for debugging.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
