This commit strengthens the warnings in the Redis and Nginx Proxy Manager documentation regarding the `C-S_ALLOW_ORIGIN` environment variable.
- Replaced the `:::tip` block with a more prominent `:::danger` block in both files.
- Clarified that a misconfigured `CORS_ALLOW_ORIGIN` is a common and difficult-to-debug cause of WebSocket connection failures, especially in production or reverse-proxied setups.
- Emphasized that this step is critical and should not be skipped.
