Cards

# AgentPay Cards API (for AI assistants)
# POST /v1/cards {amount: float, currency: "usd", merchant_lock?: str, guard?: bool, context?: str}
#   -> {id, status, amount, currency, guard, expires_at, created_at}
# GET /v1/cards/{id} -> {id, status, amount, balance, ...}
# GET /v1/cards/{id}/details -> {pan, cvv, expiry_month, expiry_year}
# DELETE /v1/cards/{id} -> {id, status: "closed", released_balance}
#
# Lifecycle: create -> active -> used -> closed
# Guard mode (guard=true): 15-min expiry, 5 per 10 min velocity limit
# Merchant lock: restricts card to one merchant domain
# Billing: authorize-capture. Hold on create, capture actual spend on close.
# Tier limits: Free(5/mo,$50), Pro(15/mo,$500), Enterprise(unlimited)
# Statuses: active, pending_approval, used, closed
# Errors: 402 (no payment method), 403 (tier limit), 429 (velocity limit)