feat: integrate auto-photo-save into item creation endpoint

- Extend ItemCreate schema with optional extracted_image_bytes (base64) and image_processing (dict)
- Update create_item endpoint to call _auto_save_photo_from_extraction after item creation
- Decode base64 image bytes and pass crop_bounds, rotation_degrees to helper
- Don't block item creation if photo save fails (log warning instead)
- Item returned with photo_path, photo_thumbnail_path populated if save succeeded
- Full backward compatibility: old clients without image fields work unchanged
- Add 5 integration tests covering all scenarios:
  - Create item WITH image_processing → photo auto-saved
  - Create item WITHOUT image_processing → no photo (backward compatible)
  - Create item WITH invalid image_processing → item created, photo skipped
  - Create item WITH crop_bounds=None → item created, photo skipped
  - Create item WITH bytes but NO processing metadata → item created, photo skipped
- All 158 backend tests passing, zero regressions

.claude/settings.local.json

@@ -90,7 +90,8 @@
       "Bash(curl -k -v https://192.168.84.131:8918/users/)",
       "Bash(curl -k -s https://192.168.84.131:8918/users/)",
       "Bash(grep -E \"\\\\.\\(tsx|ts|jsx|js\\)$\")",
-      "Bash(pkill -9 -f uvicorn)"
+      "Bash(pkill -9 -f uvicorn)",
+      "Bash(grep -E \"\\\\.\\(py|txt\\)$\")"
     ]
   }
 }