Extract still-image scene candidates from screenplay file `{source_file}`.

The screenplay language is {source_language_name} ({source_language_code}), so every free-text field in the JSON must use that same language.
Return JSON only.

Important coverage instruction:
- Use the detected heading catalog below as a checklist.
- Every output still must include the matching `heading_catalog_index`.
- Produce at least one still for each visually depictable heading catalog item.
- Add extra stills only when the same heading contains a clearly different visual beat.

Prior series memory:
{series_memory_block}

Detected screenplay scene headings:
{heading_catalog}

Full screenplay text:
{screenplay_text}