fix: kill running TRCC processes before install (PrepareToInstall)

CloseApplications wasn't reliably stopping trcc-gui.exe before file
overwrite. Added PrepareToInstall callback that force-kills both
trcc-gui.exe and trcc.exe via taskkill before copying files.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>