refactor: add type hints and FileParser.is_supported() helper

- Add return type annotation (list[str]) to Config.validate()
- Add type annotations (msg: str, -> None) to logger convenience functions
- Add FileParser.is_supported() classmethod for checking file format support

backend/app/utils/file_parser.py

@@ -63,6 +63,20 @@ class FileParser:
     
     SUPPORTED_EXTENSIONS = {'.pdf', '.md', '.markdown', '.txt'}
     
+    @classmethod
+    def is_supported(cls, file_path: str) -> bool:
+        """
+        检查文件是否为支持的格式
+        
+        Args:
+            file_path: 文件路径
+            
+        Returns:
+            如果文件格式受支持则返回 True
+        """
+        suffix = Path(file_path).suffix.lower()
+        return suffix in cls.SUPPORTED_EXTENSIONS
+    
     @classmethod
     def extract_text(cls, file_path: str) -> str:
         """