feat(llm): 新增 LLM 智能增强服务(Agnes client + 4 项 enrichment 任务 + admin API + migration)

backend/app/services/llm/__init__.py

@@ -0,0 +1,7 @@
+"""LLM 服务:客户端 + 智能增强。"""
+from app.services.llm.client import LlmClient, client  # noqa: F401
+from app.services.llm.enrichment import (  # noqa: F401
+    enrich_article,
+    enrichment_loop,
+    get_setting,
+)