fix(i18n): pass locale to background threads via thread-local storage

Background threads (graph building, simulation prep, report generation,
profile generation) now inherit the requesting user's locale preference.
Previously these fell back to 'zh' because Flask request context was
unavailable in spawned threads.

backend/app/services/oasis_profile_generator.py

@@ -20,7 +20,7 @@ from zep_cloud.client import Zep
 
 from ..config import Config
 from ..utils.logger import get_logger
-from ..utils.locale import get_language_instruction, t
+from ..utils.locale import get_language_instruction, get_locale, set_locale, t
 from .zep_entity_reader import EntityNode, ZepEntityReader
 
 logger = get_logger('mirofish.oasis_profile')
@@ -916,8 +916,12 @@ class OasisProfileGenerator:
                 except Exception as e:
                     logger.warning(f"实时保存 profiles 失败: {e}")
         
+        # Capture locale before spawning thread pool workers
+        current_locale = get_locale()
+
         def generate_single_profile(idx: int, entity: EntityNode) -> tuple:
             """生成单个profile的工作函数"""
+            set_locale(current_locale)
             entity_type = entity.get_entity_type() or "Entity"
             
             try: