feat(memory): layered architecture upgrade + remove mem0 backend (#4226)

feat(memory): layered architecture upgrade + remove mem0 backend

src/memory/postgres.rs

@@ -137,6 +137,9 @@ impl PostgresMemory {
             timestamp: timestamp.to_rfc3339(),
             session_id: row.get(5),
             score: row.try_get(6).ok(),
+            namespace: "default".into(),
+            importance: None,
+            superseded_by: None,
         })
     }
 }