Changelog

Routes: direction replaces from, and creation is idempotent

• A route now returns direction (mint-fiat, mint-stablecoin, redeem-fiat, redeem-stablecoin) instead of echoing from, and GET /v0/routes takes a direction filter.
• The stablecoin wildcard source currency is gone. Mint-from-stablecoin routes name the currency directly (today, usdc).
• POST /v0/routes is idempotent. A repeat call with the same inputs returns 200 with the existing route instead of 409 route_already_exists, which is now reserved for a route id occupied by a row the call couldn’t read back. See 200, 201, or 409.