Update frontend urls

Co-authored-by: Maximilian Dorninger <97409287+maxdorninger@users.noreply.github.com>

config.example.toml

@@ -8,7 +8,7 @@
 [misc]
 # it's very likely that you need to change this for MediaManager to work
 frontend_url = "http://localhost:3000/" # note the trailing slash
-cors_urls = ["http://localhost:3000", "http://localhost:8000"] # note the lack of a trailing slash
+cors_urls = ["http://localhost:8000"] # note the lack of a trailing slash
 
 # you probaly don't need to change this
 development = false