Add payment lifecycle API with idempotent send support

[JYZ-LESLIE]

Summary

• add fake payment routes: send, list, get, complete, and cancel
• add payment schema + database helpers for lifecycle/state transitions
• support idempotency keys in POST /payments/send to make retries safe
• add end-to-end route test covering lifecycle and idempotent replay behavior
• document the new payment routes in README

Validation

• Could not run tests in this environment because bun is not installed.

/claim #1

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 4f49104ab4

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Handle empty idempotency keys consistently

The replay guard uses a truthiness check (if (body.idempotency_key)), but the request schema allows idempotency_key: "" because it is z.string().optional(). In that case, the deduplication branch is skipped and repeated POST /payments/send calls with the same empty key create duplicate payments, which breaks the endpoint’s advertised idempotent retry behavior for this input.

Useful? React with 👍 / 👎.