add doc, add reranker option for tenant

Author: knoguchi

server/gen/openapiv2/rag/v1/tenant.swagger.json

@@ -385,6 +385,10 @@
         "systemPrompt": {
           "type": "string",
           "title": "Default system prompt for RAG queries"
+        },
+        "rerankerEnabled": {
+          "type": "boolean",
+          "description": "Enable LLM-based reranking for improved relevance.\nTrade-off: +1-3s latency, ~2x LLM cost, but better accuracy."
         }
       }
     },