Enhance table title handling and improve heading detection logic

- Added logic to set `table_title` from `caption` if it is under 160 characters and not already set.
- Updated `_blocks_from_content_list` to assign `table_title` based on `caption` length.
- Introduced new regex patterns for better detection of TOC entries and noise.
- Enhanced heading detection to differentiate between numbered instructions and actual headings.
- Added tests to verify that table captions are correctly assigned as titles and that numbered instructions are treated as body text.

backend/rag_cut/parsers/mineru_adapter.py

@@ -348,6 +348,8 @@ def _blocks_from_content_list(content_list: list[dict[str, Any]], json_path: Pat
             caption = _text_value(item)
             if caption:
                 meta["caption"] = caption
+                if len(caption) <= 160:
+                    meta["table_title"] = caption
             if src:
                 meta["source_image_path"] = str(src)
             if image_path: