feat(UME): 切换marker分页并简化告警表字段

告警同步改为按响应头 marker 连续迭代，支持 iterator is null 的500尾页兜底，同时移除告警表中的 ne_name/user_label 冗余字段，统一在查询层与网元表 join 补齐展示信息。

Co-authored-by: Cursor <cursoragent@cursor.com>

netx_api/config.py

@@ -30,6 +30,9 @@ class Settings(BaseSettings):
     ume_max_pages: int = 2000
     ume_limit_max: int = 5000
     ume_limit_only_page_size: int = 5000
+    ume_marker_page_limit: int = 1000
+    ume_marker_max_pages: int = 2000
+    ume_iterator_500_as_end: bool = True
     ume_auth_header: str = "accessToken"
     ume_content_type: str = "application/yang-data+json;charset=UTF-8"
     ume_token_ttl_s: int = 1800