feat: enable document orientation detection for scanned PDFs

- Enable PP-StructureV3's use_doc_orientation_classify feature
- Detect rotation angle from doc_preprocessor_res.angle
- Swap page dimensions (width <-> height) for 90°/270° rotations
- Output PDF now correctly displays landscape-scanned content

Also includes:
- Archive completed openspec proposals
- Add simplify-frontend-ocr-config proposal (pending)
- Code cleanup and frontend simplification

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/utils/__init__.py

@@ -0,0 +1,5 @@
+"""Utility modules for the OCR application."""
+
+from .bbox_utils import normalize_bbox, get_bbox_center, calculate_ioa
+
+__all__ = ['normalize_bbox', 'get_bbox_center', 'calculate_ioa']