feat(i18n): replace hardcoded Chinese in backend SSE progress messages

backend/app/models/task.py

@@ -10,6 +10,8 @@ from enum import Enum
 from typing import Dict, Any, Optional
 from dataclasses import dataclass, field
 
+from ..utils.locale import t
+
 
 class TaskStatus(str, Enum):
     """任务状态枚举"""
@@ -148,7 +150,7 @@ class TaskManager:
             task_id,
             status=TaskStatus.COMPLETED,
             progress=100,
-            message="任务完成",
+            message=t('progress.taskComplete'),
             result=result
         )
     
@@ -157,7 +159,7 @@ class TaskManager:
         self.update_task(
             task_id,
             status=TaskStatus.FAILED,
-            message="任务失败",
+            message=t('progress.taskFailed'),
             error=error
         )