Retry failed orders in a multiswap

Retry a failed multiswap bundle. Only possible while the orders are within 30 minutes of creation (deposit addresses still valid) — the existing UserOp is reset to PENDING and txData (same shape as POST multi/{multiId}/tx/build) is returned so the frontend can re-sign and submit immediately.

After 30 minutes, or for REFUNDED orders, this returns 400 — use POST /multi/recovery to withdraw the stuck funds instead.