Initial snapshot before step 6 options.js split

host/rcjav-host.bat

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+@echo off
+REM Portable: uses Windows py launcher if present, falls back to python on PATH.
+REM Stderr redirected to log file so it can't pollute stdout (native messaging is binary).
+setlocal
+set "PYBIN=python"
+where py >nul 2>&1 && set "PYBIN=py"
+if not exist "%~dp0logs" mkdir "%~dp0logs"
+"%PYBIN%" -u "%~dp0rcjav-host.py" 2>>"%~dp0logs\rcjav-host-stderr.log"