left_sidebar: Don't fade inactive channels (unless muted).

Part of #35552.

web/src/stream_list.ts

@@ -531,6 +531,9 @@ class StreamSidebarRow {
         this.update_unread_count();
     }
 
+    // The `inactive_stream` class is useful for identifying these
+    // channels to node tests, even if the design doesn't currently
+    // style these channels differently.
     update_whether_active(): void {
         if (stream_list_sort.has_recent_activity(this.sub)) {
             this.$list_item.removeClass("inactive_stream");