Send email from Windsurf

Add transactional email to this project using emails.sh.

Read https://emails.sh/docs.md first so you use the real request shape instead of guessing it.

1. Run `npm install @emails.sh/sdk` in the project root.
2. Add EMAILSSH_API_KEY to the env file this project already uses, and check that file is gitignored. If I have not given you a key, stop and tell me to create one at https://emails.sh/dashboard instead of inventing a placeholder.
3. Add one server-side module that builds the client from process.env.EMAILSSH_API_KEY and exports a send function. Do not call the API from client code.
4. Call it from the signup handler to send a verification email, from onboarding@emails.sh until my domain is verified.
5. List the files you changed and the environment variables I still need to set on my host.

import { Emailssh } from '@emails.sh/sdk';

const emails = new Emailssh(process.env.EMAILSSH_API_KEY!);

interface Receipt {
	email: string;
	orderId: string;
	amount: string;
}

export async function sendReceipt({ email, orderId, amount }: Receipt) {
	const { id } = await emails.send({
		from: 'Acme <billing@acme.com>',
		to: [email],
		// reply_to matters on a receipt: the reply goes to a person, not to a
		// no-reply address the customer has to work around.
		replyTo: 'support@acme.com',
		subject: `Receipt for order ${orderId}`,
		html: `<p>Thanks for your order.</p><p>Order ${orderId}, ${amount}.</p>`,
		text: `Thanks for your order. Order ${orderId}, ${amount}.`,
		tags: { type: 'receipt' },
		// One receipt per order, even if the payment webhook is delivered twice.
		idempotencyKey: `receipt:${orderId}`
	});

	return id;
}

To:      customer@example.com
Subject: Receipt for order 10428

Thanks for your order. Order 10428, $24.00.