Send an event to Inngest and deduplicate it idempotently with an event id

Documented steps

1. Install and instantiate the client: `npm i inngest`, then `export const inngest = new Inngest({ id: "my-app" })`. Only `id` is required. Ref: https://www.inngest.com/docs/reference/client/create
2. Set `INNGEST_EVENT_KEY` in the environment for production sends (or pass `eventKey` to the client constructor). Event keys are NOT required against the local Dev Server. Ref: https://www.inngest.com/docs/events
3. Send one or many events: `const { ids } = await inngest.send([{ name: "app/invoice.created", data: { invoiceId } }])`. `send()` accepts a single payload or an array and returns `{ ids: string[] }`. Ref: https://www.inngest.com/docs/reference/events/send
4. Payload fields: `name` (required, lowercase dot notation), `data` (required, JSON-serializable), `id` (optional dedup key), `ts` (optional ms timestamp), `v` (optional payload version string such as "2023-04-14.1").
5. For idempotency, set a deterministic `id` on the payload, e.g. `id: `invoice-created-${invoiceId}``. Inngest ignores any later event carrying an id it has already seen, regardless of the payload body.
6. Verify delivery in the Dev Server UI at http://localhost:8288 or in the Inngest dashboard's Events view; the returned `ids` array maps 1:1 to the payloads you sent.