Split class-image-prompt-builder.php (331 lines) into two files:
- class-image-prompt-builder.php (now ~300 lines)
- class-image-scene-parser.php (~91 lines) with three public static methods:
- parse_scene_and_caption()
- extract_first_paragraph()
- synthesize_visual_concepts_fallback()
Builder now calls these via PRAutoBlogger_Image_Scene_Parser:: static calls.
Maintains identical external behavior; internal refactor only.
Target: prevents CI violations when adding Opik instrumentation.
