26.6.0

JDK 25 now required for Teku 26.6.0 — nodes fail to start otherwise. 26.6.1 fixes chain-following issues, identical except older snappy library. Added Gloas POST /eth/v1/beacon/states/{state_id}/builders endpoint; renamed two execution payload REST endpoints. Fixed external signer slashing protection, IPv6 detection, sync committee retries. Windows support removed next release.