purple: prevent screen dismiss on purple welcome view

Suggested-by: Daniel Daquino <daniel@daquino.me>
Signed-off-by: William Casarin <jb55@jb55.com>

damus/Views/Purple/DamusPurpleWelcomeView.swift

@@ -122,6 +122,7 @@ struct DamusPurpleWelcomeView: View {
             })
             
         })
+        .interactiveDismissDisabled()
     }
 }