feat(dlob): support two sources + per-user switch

- Add "source" column + composite PKs for DLOB tables\n- Filter public Hasura selects by X-Hasura-Dlob-Source\n- Run parallel workers for mevnode + dlob.drift.trade\n- Frontend proxy sets x-hasura-dlob-source from cookie and injects UI switch

kustomize/base/dlob-worker/deployment.yaml

@@ -26,6 +26,8 @@ spec:
                 secretKeyRef:
                   name: trade-hasura
                   key: HASURA_GRAPHQL_ADMIN_SECRET
+            - name: DLOB_SOURCE
+              value: mevnode
             - name: DLOB_HTTP_URL
               value: http://dlob-server:6969
             - name: DLOB_MARKETS