fix: auto-fix code issues (cron)

- 修复重复导入/字段
- 修复异常处理
- 修复PEP8格式问题
- 添加类型注解

backend/image_processor.py

@@ -93,7 +93,7 @@ class ImageProcessor:
         "other": "其他",
     }
 
-    def __init__(self, temp_dir: str = None):
+    def __init__(self, temp_dir: str = None) -> None:
         """
         初始化图片处理器
 
@@ -103,7 +103,7 @@ class ImageProcessor:
         self.temp_dir = temp_dir or os.path.join(os.getcwd(), "temp", "images")
         os.makedirs(self.temp_dir, exist_ok=True)
 
-    def preprocess_image(self, image, image_type: str = None):
+    def preprocess_image(self, image, image_type: str = None) -> None:
         """
         预处理图片以提高OCR质量
 
@@ -145,7 +145,7 @@ class ImageProcessor:
             print(f"Image preprocessing error: {e}")
             return image
 
-    def _enhance_whiteboard(self, image):
+    def _enhance_whiteboard(self, image) -> None:
         """增强白板图片"""
         # 转换为灰度
         gray = image.convert("L")
@@ -160,7 +160,7 @@ class ImageProcessor:
 
         return binary.convert("L")
 
-    def _enhance_handwritten(self, image):
+    def _enhance_handwritten(self, image) -> None:
         """增强手写笔记图片"""
         # 转换为灰度
         gray = image.convert("L")