NS Structured Prompt List

Parses a JSON string and emits two parallel STRING lists (prompts and filename_prefixes) so the downstream graph runs once per item. - **items_path**: dotted JSON path to the array. Default `items` matches `{"items": [...]}`. Leave empty if the JSON root is already an array. - **prompt_field** / **filename_field**: keys to extract from each item. Strips ```json fences if the upstream LLM wrapped its output. Raises a clear error if the JSON is malformed or the fields/path don't resolve.