feat: add initial People Playground mod development kit

extracted_wiki_content/internalReference/pianodialogbox.txt

@@ -0,0 +1,24 @@
+URL: https://wiki.studiominus.nl/internalReference/PianoDialogBox.html
+Title: People Playground Modding - PianoDialogBox
+==================================================
+
+public class PianoDialogBox
+Inherits MonoBehaviour
+Controls the piano dialog box
+Fields
+public static BellClip SelectedBellClip
+The most recently selected bell clip from the piano UI
+
+Properties
+public static PianoDialogBox Instance { get; private set; }
+The main instance of this singleton
+
+Methods
+public static void Show(BellClip startClip, System.Action<BellClip> onApply)
+Show the dialog box given a default selection and the callback when Apply is clicked
+
+public static void Hide()
+Hide the dialog box
+
+public void ApplyClicked()
+No description provided