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/services/pp_structure_debug.py

@@ -15,6 +15,8 @@ from datetime import datetime
 
 from PIL import Image, ImageDraw, ImageFont
 
+from app.utils.bbox_utils import normalize_bbox
+
 logger = logging.getLogger(__name__)
 
 # Color palette for different element types (RGB)
@@ -238,42 +240,8 @@ class PPStructureDebug:
         draw.text((legend_x + 18, legend_y), "raw_ocr", fill=(0, 0, 0), font=font)
 
     def _normalize_bbox(self, bbox: Any) -> Optional[Tuple[float, float, float, float]]:
-        """Normalize bbox to (x0, y0, x1, y1) format."""
-        if not bbox:
-            return None
-
-        try:
-            # Handle nested list format [[x1,y1], [x2,y2], [x3,y3], [x4,y4]]
-            if isinstance(bbox, (list, tuple)) and len(bbox) >= 1:
-                if isinstance(bbox[0], (list, tuple)):
-                    xs = [pt[0] for pt in bbox if len(pt) >= 2]
-                    ys = [pt[1] for pt in bbox if len(pt) >= 2]
-                    if xs and ys:
-                        return (min(xs), min(ys), max(xs), max(ys))
-
-            # Handle flat list [x0, y0, x1, y1]
-            if isinstance(bbox, (list, tuple)) and len(bbox) == 4:
-                return (float(bbox[0]), float(bbox[1]), float(bbox[2]), float(bbox[3]))
-
-            # Handle flat polygon [x1, y1, x2, y2, ...]
-            if isinstance(bbox, (list, tuple)) and len(bbox) >= 8:
-                xs = [bbox[i] for i in range(0, len(bbox), 2)]
-                ys = [bbox[i] for i in range(1, len(bbox), 2)]
-                return (min(xs), min(ys), max(xs), max(ys))
-
-            # Handle dict format
-            if isinstance(bbox, dict):
-                return (
-                    float(bbox.get('x0', bbox.get('x_min', 0))),
-                    float(bbox.get('y0', bbox.get('y_min', 0))),
-                    float(bbox.get('x1', bbox.get('x_max', 0))),
-                    float(bbox.get('y1', bbox.get('y_max', 0)))
-                )
-
-        except (TypeError, ValueError, IndexError) as e:
-            logger.warning(f"Failed to normalize bbox {bbox}: {e}")
-
-        return None
+        """Normalize bbox to (x0, y0, x1, y1) format. Uses shared bbox utility."""
+        return normalize_bbox(bbox)
 
     def _generate_summary(
         self,