chore: rename css piano (#44210)

* chore: rename files

* chore: update codebase

* chore: proper title case

curriculum/challenges/_meta/learn-responsive-web-design-by-building-a-piano/meta.json

@@ -1,8 +1,8 @@
 {
-  "name": "CSS Piano",
+  "name": "Learn Responsive Web Design by Building a Piano",
   "isUpcomingChange": true,
   "usesMultifileEditor": true,
-  "dashedName": "css-piano",
+  "dashedName": "learn-responsive-web-design-by-building-a-piano",
   "order": 13,
   "time": "5 hours",
   "template": "",