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/simulation_runner.py

@@ -20,6 +20,7 @@ from queue import Queue
 
 from ..config import Config
 from ..utils.logger import get_logger
+from ..utils.locale import get_locale, set_locale
 from .zep_graph_memory_updater import ZepGraphMemoryManager
 from .simulation_ipc import SimulationIPCClient, CommandType, IPCResponse
 
@@ -455,10 +456,13 @@ class SimulationRunner:
             cls._processes[simulation_id] = process
             cls._save_run_state(state)
             
+            # Capture locale before spawning monitor thread
+            current_locale = get_locale()
+
             # 启动监控线程
             monitor_thread = threading.Thread(
                 target=cls._monitor_simulation,
-                args=(simulation_id,),
+                args=(simulation_id, current_locale),
                 daemon=True
             )
             monitor_thread.start()
@@ -475,8 +479,9 @@ class SimulationRunner:
         return state
     
     @classmethod
-    def _monitor_simulation(cls, simulation_id: str):
+    def _monitor_simulation(cls, simulation_id: str, locale: str = 'zh'):
         """监控模拟进程，解析动作日志"""
+        set_locale(locale)
         sim_dir = os.path.join(cls.RUN_STATE_DIR, simulation_id)
         
         # 新的日志结构：分平台的动作日志