Fix MudBlazor dialog and input issues in Pro modules #22640
BackMarshal MudBlazor dialog, message and focus calls back to the Blazor dispatcher, since release builds move continuations off it after remote calls. The duplicated import message is fixed by closing the import dialog before showing the result, because MudBlazor 9.4 recreates remaining dialogs when another one closes. Also restores the upload dialog drop area, adds Enter-to-save, and makes the chat input Immediate.