[Enhancement]: Add installer option for case-insensitive optional directories

### Problem / Motivation

Some games, particularly Windows games running through compatibility layers such as Wine/Proton, may require or benefit from case-insensitive filename handling.

Linux filesystems are normally case-sensitive, which can cause compatibility issues when a game expects paths such as:

Textures/Block.png

to be equivalent to:

textures/block.png

CachyOS could make this easier to configure during installation by adding an optional installer feature.

### Proposed Solution

Add the following option to the installer:

Enable case-insensitive optional directories

This would allow users to configure specific directories as case-insensitive without changing the behavior of the entire filesystem.

For example, the user could create a dedicated directory for games that require this behavior:

/home//Games

or another directory of their choice.

### Alternatives Considered

I have not found any alternatives

### Additional Context

Some games may fail to locate assets, configuration files, or other resources because of differences in filename capitalization.

Having an easily configurable case-insensitive directory would allow users to install or move those games into a suitable location without manually configuring filesystem features after installation.

Requirements

The feature should only affect directories explicitly selected/configured by the user.

Normal Linux directories should remain case-sensitive.

The installer should detect whether the selected filesystem supports the required casefold functionality.

ext4's native casefold support could be used where available.

The installer should clearly warn the user if the selected filesystem does not support the feature.

Users should be able to create/configure additional case-insensitive directories after installation if needed.

Start by locating the installer entry point and reviewing how it detects filesystem capabilities and configures optional directories. Check ext4 casefold support and the behavior on unsupported filesystems. Done means users can select directories, receive a clear warning when unsupported, preserve normal case-sensitive directories, and have a documented post-installation path for adding more directories.

Written by the indexing model from the issue text.