suppress the restricted NavController.currentBackStack in navigateDetail

currentBackStack is @RestrictTo(LIBRARY_GROUP), which CI's Android Lint rejected. There is
no public API that matches a back-stack entry by its arguments, so keep it and suppress the
check rather than fall back to argument-blind popBackStack(route).

app/src/main/kotlin/com/subtracks/ui/AppRoot.kt

@@ -197,6 +197,9 @@ private fun MainNavigation() {
             }
     }
 
+    // currentBackStack is restricted to androidx.navigation, but it is the only way to find a
+    // detail entry by its arguments; popBackStack(route) matches the destination and ignores them.
+    @Suppress("RestrictedApi")
     fun navigateDetail(
         pattern: String,
         argument: String,