Add themes directory to file_types

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From Ghostty's man page:

Two different directories will be searched for themes.

• The first directory is the themes subdirectory of your Ghostty configuration directory. This is $XDG_CONFIG_HOME/ghostty/themes or ~/.config/ghostty/themes.

• The second directory is the themes subdirectory of the Ghostty resources directory. Ghostty ships with a multitude of themes that will be installed into this directory. On macOS, this directory is the Ghostty.app/Contents/Resources/ghostty/themes. On Linux, this directory is the share/ghostty/themes (wherever you installed the Ghostty “share” directory). If you’re running Ghostty from the source, this is the zig-out/share/ghostty/themes directory.

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@Else00 Bump