refactor(core): 重构异常处理以使用统一处理器并改进代码组织

将基于列表的异常处理器替换为基于字典的 EXCEPTION_MAPPINGS，以提高可维护性
将多个处理函数合并为单个 unified_exception_handler，以实现一致的错误响应
删除异常类定义之间不必要的空行
添加全面的文档字符串，解释异常注册和统一处理器的行为
简化异常处理器注册循环，直接遍历映射的异常类
通过更清晰的变量命名改进类型提示和代码可读性

app/core/exceptions.py

@@ -1,42 +1,45 @@
 from fastapi import FastAPI, Request
 from fastapi.responses import JSONResponse
 
-
 class DocumentNotFoundError(Exception):
     def __init__(self, document_id: str):
         super().__init__(f"Document '{document_id}' not found")
 
-
 class DocumentParseError(Exception):
     """Word 下载或解析失败。"""
     pass
 
-
 class ExportError(Exception):
     pass
 
-
 class RecordNotFoundError(Exception):
     def __init__(self, record_id: str):
         super().__init__(f"Export record '{record_id}' not found")
 
-
-_HANDLERS: list[tuple[type[Exception], int, int]] = [
-    (DocumentNotFoundError, 404, 404),
-    (DocumentParseError,    400, 400),
-    (ExportError,           500, 500),
-    (RecordNotFoundError,   404, 4041),
-]
-
+# 异常映射配置：异常类 -> (HTTP状态码, 业务错误码)
+EXCEPTION_MAPPINGS: dict[type[Exception], tuple[int, int]] = {
+    DocumentNotFoundError: (404, 404),
+    DocumentParseError: (400, 400),
+    ExportError: (500, 500),
+    RecordNotFoundError: (404, 4041),
+}
 
 def register_exception_handlers(app: FastAPI) -> None:
-    def _make_handler(http_status: int, code: int):
-        async def handler(request: Request, exc: Exception) -> JSONResponse:
-            return JSONResponse(
-                status_code=http_status,
-                content={"code": code, "message": str(exc), "data": None},
-            )
-        return handler
-
-    for exc_class, http_status, code in _HANDLERS:
-        app.add_exception_handler(exc_class, _make_handler(http_status, code))
+    """注册全局异常处理器，所有自定义异常返回标准格式：{"code": int, "message": str, "data": None}"""
+    async def unified_exception_handler(request: Request, exc: Exception) -> JSONResponse:
+        """统一异常处理函数"""
+        # 从映射中获取配置，如果不存在则使用默认值 (500, 500)
+        http_status, error_code = EXCEPTION_MAPPINGS.get(type(exc), (500, 500))
+        
+        return JSONResponse(
+            status_code=http_status,
+            content={
+                "code": error_code,
+                "message": str(exc),
+                "data": None,
+            },
+        )
+    
+    # 为所有配置的异常类型注册同一个处理函数
+    for exc_class in EXCEPTION_MAPPINGS:
+        app.add_exception_handler(exc_class, unified_exception_handler)