feat: implement Phase 1 of PDF layout restoration

Implement critical fixes for image and table rendering in PDF generation.

**Image Handling Fixes**:
- Implemented _save_image() in pp_structure_enhanced.py
  - Creates imgs/ subdirectory for saved images
  - Handles both file paths and numpy arrays
  - Returns relative path for reference
  - Adds proper error handling and logging
- Added saved_path field to image elements for path tracking
- Created _get_image_path() helper with fallback logic
  - Checks saved_path, path, image_path in content
  - Falls back to metadata fields
  - Logs warnings for missing paths

**Table Rendering Fixes**:
- Fixed table rendering to use element's own bbox directly
  - No longer depends on fake table_*.png references
  - Supports both bbox and bbox_polygon formats
  - Inline conversion for different bbox formats
- Maintains backward compatibility with legacy approach
- Improved error handling for missing bbox data

**Status**:
- Phase 1 tasks 1.1 and 1.2: ✅ Completed
- Phase 1 tasks 2.1, 2.2, and 2.3: ✅ Completed
- Testing pending due to backend availability

These fixes resolve the critical issues where images never appeared
and tables never rendered in generated PDFs.

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

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

backend/app/services/pp_structure_enhanced.py

@@ -259,8 +259,12 @@ class PPStructureEnhanced:
             elif mapped_type in [ElementType.IMAGE, ElementType.FIGURE]:
                 # Save image if path provided
                 if 'img_path' in item and output_dir:
-                    self._save_image(item['img_path'], output_dir, element['element_id'])
-                    element['img_path'] = item['img_path']
+                    saved_path = self._save_image(item['img_path'], output_dir, element['element_id'])
+                    if saved_path:
+                        element['saved_path'] = saved_path
+                        element['img_path'] = item['img_path']  # Keep original for reference
+                    else:
+                        logger.warning(f"Failed to save image for element {element['element_id']}")
 
             # Add any additional metadata
             if 'metadata' in item:
@@ -411,13 +415,54 @@ class PPStructureEnhanced:
             return list(map(int, match.groups()))
         return [0, 0, 0, 0]
 
-    def _save_image(self, img_path: str, output_dir: Path, element_id: str):
-        """Save image file to output directory."""
+    def _save_image(self, img_path: str, output_dir: Path, element_id: str) -> Optional[str]:
+        """Save image file to output directory and return relative path.
+
+        Args:
+            img_path: Path to image file or image data
+            output_dir: Base output directory for results
+            element_id: Unique identifier for the element
+
+        Returns:
+            Relative path to saved image, or None if save failed
+        """
+        import shutil
+        import numpy as np
+        from PIL import Image
+
         try:
-            # Implementation depends on how images are provided
-            pass
+            # Create imgs subdirectory
+            img_dir = output_dir / "imgs"
+            img_dir.mkdir(parents=True, exist_ok=True)
+
+            # Determine output file path
+            dst_path = img_dir / f"{element_id}.png"
+            relative_path = f"imgs/{element_id}.png"
+
+            # Handle different input types
+            if isinstance(img_path, str):
+                src_path = Path(img_path)
+                if src_path.exists() and src_path.is_file():
+                    # Copy existing file
+                    shutil.copy2(src_path, dst_path)
+                    logger.info(f"Copied image from {src_path} to {dst_path}")
+                else:
+                    logger.warning(f"Image file not found: {img_path}")
+                    return None
+            elif isinstance(img_path, np.ndarray):
+                # Save numpy array as image
+                Image.fromarray(img_path).save(dst_path)
+                logger.info(f"Saved numpy array image to {dst_path}")
+            else:
+                logger.warning(f"Unknown image type: {type(img_path)}")
+                return None
+
+            # Return relative path for reference
+            return relative_path
+
         except Exception as e:
-            logger.warning(f"Failed to save image {img_path}: {e}")
+            logger.error(f"Failed to save image for element {element_id}: {e}")
+            return None
 
     def _save_pil_image(self, img_obj, output_dir: Path, element_id: str):
         """Save PIL image object to output directory."""