Server option does not fully lock the port.

`--server` option starts the server on port `3000` but still this port is accessible by other apps.
- I can start `aglio` even when the port is already taken by another process. (Tried with `node`). In this case, request will be served by the node app.
- I can start another process (Tried with `node`) even when `aglio` is running on the same port. In this case, request will be served by the `aglio` app.
- `node` is not allowing to start another `node` process if port is already taken.

What could be the issue. Ideally the second process should have failed with `Port is already taken`.

Start at the `--server` option handling and the code that binds port `3000`. Reproduce the issue with `aglio` and another Node process using the same port, then trace why both processes start. Done means a second process fails with a clear `Port is already taken` error instead of serving requests through either app.

Written by the indexing model from the issue text.