stepSeconds required for queryType 'range'

Should we update the doc string to specific that `stepSeconds` are required for 'range' queries? Running into a case now where that was not clear to the LLM based on the current doc: https://github.com/grafana/mcp-grafana/blob/03027288f63bfef7b3ac506d33ca32ba52eb9935/tools/prometheus.go#L84

![Image](https://github.com/user-attachments/assets/49e2b6b1-f223-45e6-bddf-fdfb2ec48e07)