Send email from a Replit app

Add transactional email to this Repl using emails.sh so signing up sends a verification email.

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

Requirements:
- Install the SDK (npm install @emails.sh/sdk for node, pip install emailssh for python).
- Read the key from the environment variable EMAILSSH_API_KEY. I will add it in the Secrets pane. Do not write the key into any file, do not print it, and if it is missing at runtime raise an error that names the variable.
- Do the send in server-side code only, never in code that runs in the browser.
- Send from onboarding@emails.sh until I verify my own domain.
- Tell me the exact secret name to add when you are done.

import os
import uuid

from emailssh import Emailssh
from flask import Flask, request, jsonify

app = Flask(__name__)

# Reading the secret at startup means a missing value fails immediately, not
# on the first signup at three in the morning.
api_key = os.environ.get("EMAILSSH_API_KEY")
if not api_key:
    raise RuntimeError("EMAILSSH_API_KEY is not set. Add it in the Secrets pane.")

emails = Emailssh(api_key)


@app.post("/signup")
def signup():
    email = request.json["email"]
    token = str(uuid.uuid4())
    link = f"https://acme.com/verify?token={token}"

    result = emails.send(
        from_="Acme <onboarding@emails.sh>",
        to=[email],
        subject="Confirm your email",
        html=f'<p>Confirm your address.</p><p><a href="{link}">Confirm your email</a></p>',
        text=f"Confirm your address: {link}",
        idempotency_key=f"verify:{token}",
    )

    return jsonify({"email_id": result["id"]})


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=8080)

To:      student@example.com
Subject: Confirm your email

Confirm your address: https://acme.com/verify?token=e40a72