When the LLM returns an empty completion, gateway/run.py replaced
final_response with the literal string '(No response generated)'.
This defeated cron/scheduler.py's empty-response skip guard, causing
the placeholder to be delivered to home channels.
Changes:
- gateway/run.py: return empty string instead of placeholder when
there is no error and no response content
- cron/scheduler.py: defensively strip the placeholder text in case
any upstream path still produces it
FixesNousResearch/hermes-agent#9270