Update _category_.json (#2442)

### What problem does this PR solve?

#2441 

### Type of change

- [x] Documentation Update

docs/guides/agentic_rag/_category_.json

 {
-  "label": "Agentic RAG",
+  "label": "Agents",
   "position": 3,
   "link": {
     "type": "generated-index",
-    "description": "RAGFlow v0.8.0 introduces an Agentic RAG mechanism, featuring a no-code workflow editor on the front end and a comprehensive graph-based task orchestration framework on the back end."
+    "description": "RAGFlow v0.8.0 introduces an agent mechanism, featuring a no-code workflow editor on the front end and a comprehensive graph-based task orchestration framework on the back end."
   }
 }