docs(migration): correct migration guides to match v3 (update available, no async_mode/graph_store/offset)

docs/docs.json

@@ -1147,6 +1147,10 @@
     {
       "source": "/openmemory/integrations",
       "destination": "/introduction"
+    },
+    {
+      "source": "/migration/api-changes",
+      "destination": "/migration/platform-v2-to-v3"
     }
   ]
 }