[Install] Allowing voice-only mod to be installed ontop of full mod manifests as crash when opening video played

Currently, the umineko installer doesn't support installing the voice-only mod ontop of the full mod (or vice-versa)

This is because the installer doesn't delete/restore files, it only ever overwrites/adds new files.

So if you try to install voice-only ontop of the full mod, files such as the high-res movie files will be "left over" form the full mod.

This will cause a crash when the voice-only mod attempts to play them, due to the resolution difference.

There is a minor popup in the installer if this is detected, but it's probably better to outright disallow installation, since we've had multiple reports of this problem happening before.

So I would change:

- On the installer for Umineko, if you attempt to change from full to voice only or vice versa, instead of showing you install options, it should show instructions, telling you to:
- Delete the whole game folder (copy instructions from FAQ on how to do this)
- Re-install the game
- Refresh the webpage (hit ctrl-r) or restart the installer
- It also may be possible to add a check to the voice-only script (eg "if this full mod file exists, show a warning message"), but it's been so long I've touched any nScripter I can't really be bothered, I might mess something up.

Look at the Umineko installer code, likely in a C# project, to find where mod installation options are presented. Identify the check for existing mod files and the popup logic. Modify to detect a switch between full and voice-only mods and show instructions instead. Test by simulating both mod installation states.

Written by the indexing model from the issue text.