As an experienced Commons user, I want to be able to filter my search on the Categories and Pages tab by namespace, so that I can find what I'm looking for without having to filter through too many results.
As we try to bring more functionality that is currently possible on special:search to Media Search, we want to add a Namespace filter to the Categories and Pages tab. It won't be a dropdown/select like the other filters but a dialog instead to allow for more complex interactions and more space to use comfortably.
Design: desktop and mobile (current special:search for reference at the top)
 Crete a dialog that allows the user to select their preferred namespaces
 Dialog options include 4 radio buttons: All, Discussion, General Help, and Custom
 Nested underneath the Custom radio button is all of the available namespaces for the tab, and they should be able to be selected individually as checkboxes. The user should be able to select as many as they'd like.
 Mobile web is a full screen dialog
 Default is no longer an option
 "Remember selection..." is no longer an option
 If the user clicks "Submit", the search on the Categories and Pages tab should be filtered to only include their selected namespaces
 The user can click the "X" in the upper right hand corner to dismiss the dialog //without// saving their selections. The search results should not change.