feat(backend,frontend): copy liked songs into a shareable playlist

backend/.env.example

@@ -11,3 +11,8 @@ API__HOST=0.0.0.0
 API__PORT=8080
 API__WORKERS=1
 API__DOCS=false
+
+PUBLIC_URL=http://127.0.0.1:5173
+SPOTIFY__CLIENT_ID=
+SPOTIFY__CLIENT_SECRET=
+SESSION__SECRET=