-- Migration 011: Add HMAC column for purchase key verification.
-- Enables HMAC-based time-gated key release without storing the original key in the URL.
-- sender_key_hmac: HMAC-SHA256(senderDecryptionKey, tmpKey + issuedAt timestamp)
-- sender_key_issued_at: when the purchase key was issued (for 5-min window check)
ALTER TABLE customers
  ADD COLUMN IF NOT EXISTS sender_key_hmac      TEXT,
  ADD COLUMN IF NOT EXISTS sender_key_issued_at TIMESTAMPTZ;
