Only put an emoji in a step name if the user asked for one

We are keeping emojis allowed in step names. Someone who wants one should be able to have it, and if they ask for one we should give it to them.

What we would rather avoid is Apollo adding them to names nobody asked for. A user typing an emoji is a choice they made. The AI decorating a generated workflow spreads them around for no benefit, and makes the conflict in OpenFn/lightning#5156 more likely to be hit by someone who never opted into it.

The rule the model sees is built in describe_rule in services/name_rules.py, so this is a wording change rather than validation. Something like telling it to write the name the user asked for and not to decorate it. We should not strip emojis after the fact, because we cannot tell one the user asked for from one the model invented.

Worth checking against the workflow_chat acceptance tests, since they are the only way to see whether a prompt change actually moved the model.

Related: OpenFn/lightning#5156, OpenFn/apollo#446.

Start in services/name_rules.py at describe_rule and review the wording that guides generated step names. Update the rule so user-provided emojis remain allowed while unrequested emojis are not added, then run the workflow_chat acceptance tests to verify the prompt change affects generated names.