Selecting a directory in filepicker model

**Describe the bug**
I'm not sure if this is possible with the existing model, but there doesn't appear to be any documentation on how to pick directories on the filepicker component. The component looks phenomenonal, but even setting the `DirAllowed` to true and the `FileAllowed` to false, files are still shown and directories can't be selected, at least in any obvious way. The component looks phenomenal, but I'm unsure of how to use the component to select only directories.

**Setup**
Please complete the following information along with version numbers, if applicable.
- OS MacOs Sonoma
- Shell zsh
- Terminal Emulator iterm
- Terminal Multiplexer tmux

**To Reproduce**
Steps to reproduce the behavior:
```go
func InitialFilePicker() *model {
fp := filepicker.New()
fp.DirAllowed = true
fp.FileAllowed = false
fp.AllowedTypes = []string{}
fp.AutoHeight = true
fp.CurrentDirectory, _ = os.UserHomeDir()
m := model{
filepicker: fp,
err: nil,
}
return &m
}
```

**Source Code**
See Above

**Expected behavior**
To be able to select directories, and to hide files in the options list.

**Additional context**
I'm very new to Go, but don't feel that this is a code issue, as the app in it's current state is super simple

Start at the filepicker component entry point used by filepicker.New and trace how DirAllowed, FileAllowed, and AllowedTypes affect the displayed entries and selection behavior. Reproduce the supplied configuration, then verify that directory-only mode permits directory selection and hides files.

Written by the indexing model from the issue text.