No setting to disable "submit on empty Enter" behavior — should be user-configurable

The chat input has a behavior where pressing Enter on an empty input triggers a default action/submit. This can be a useful feature for some workflows, but it's a liability for others — an accidental Enter mid-session can trigger an unwanted request.

The issue isn't the feature itself, but that there is no way to disable it. This should be exposed as a user-configurable setting (e.g. in settings.json) so users can opt out if they prefer Enter on an empty input to be a no-op.

Request: Add a setting to control whether pressing Enter on empty input triggers the default action, or does nothing.