T4: rollback.exe — New Native Executable

[Varaniya201]

1. Implement idempotent JRE restore: jre11/ → jre/
2. Implement jre21_temp/ cleanup
3. Implement run.bat restore from run.bat_jre11
4. Implement .TEMP/ cleanup
5. Implement operator dialog on completion
6. Verify ./MANIFEST.MF is untouched (version mismatch preserved for retry)