fix: sync removes users that no longer exist on Volcengine

- Track all Volcengine usernames during sync
- Delete local users not found on Volcengine (cascade deletes related data)
- Report removed users in sync response
- Deleted test_audit and tudouceshi from local DB

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/apps/monitor/views.py

@@ -184,6 +184,7 @@ def iam_user_sync_view(request):
 
     svc = IAMService(ak, sk)
     imported = []
+    volc_usernames = set()
     offset = 0
 
     while True:
@@ -199,6 +200,7 @@ def iam_user_sync_view(request):
 
         for u in users:
             username = u.get("UserName", "")
+            volc_usernames.add(username)
             obj, created = IAMUser.objects.update_or_create(
                 volc_account=account,
                 username=username,
@@ -253,10 +255,22 @@ def iam_user_sync_view(request):
         if offset >= total:
             break
 
+    # 删除火山已不存在的用户（本地有但火山没有）
+    removed = []
+    local_users = IAMUser.objects.filter(volc_account=account)
+    for local_user in local_users:
+        if local_user.username not in volc_usernames:
+            removed.append(local_user.username)
+            local_user.delete()
+
     total_count = IAMUser.objects.filter(volc_account=account).count()
+    msg = f'同步完成，共 {total_count} 个用户，新导入 {len(imported)} 个'
+    if removed:
+        msg += f'，清理 {len(removed)} 个已删除用户（{", ".join(removed)}）'
     return Response({
-        'message': f'同步完成，共 {total_count} 个用户，新导入 {len(imported)} 个',
+        'message': msg,
         'imported': imported,
+        'removed': removed,
         'total': total_count,
     })