#12)

The relayer expects 'owner' as a top-level field in the batch
redemption payload, but request_batch_ctf_redemption was only
sending { chainId, redemptions }. This caused the relayer to
return 'Invalid owner address format'.

Now includes the signer's address as 'owner' in the request body,
matching the frontend's request format:
  { chainId, owner, redemptions }

Also adds _require_signer() check since owner comes from the signer.