Extract text blocks from this document image. A text block is a visually distinct group of text separated from other text by whitespace or graphical elements.

For each text block, provide:
- bbox_2d: [x1, y1, x2, y2] bounding box coordinates
- text_content: Complete text of the block (multiple lines joined with space)
- is_bold: true if text appears bold
- font_size: "small", "normal", or "large"

Important:
- Merge consecutive lines that form a single paragraph into ONE text block
- Keep separate blocks for: headers, titles, different sections, footer

Output format: JSON array
[{"bbox_2d": [x1,y1,x2,y2], "text_content": "...", "is_bold": false, "font_size": "normal"}, ...]