Send SMS with Bun

Add SMS sending to this Bun project with TextKit.

- Docs for this stack: https://jointextkit.com/docs/send-with-bun.md
- API: POST https://api.jointextkit.com/v1/messages with `Authorization: Bearer
  <key>` and a JSON body `{"to": "+1...", "body": "..."}`.
- Use the official SDK: `bun add jointextkit`, then `new
  TextKit().messages.send({ to, body })`.
- Read the key from the `TEXTKIT_API_KEY` environment variable. Never hardcode
  it or send it to the browser.
- Phone numbers are E.164 and US or Canada only (`+1` followed by 10 digits).
- A test key (`ssms_sk_test_`) simulates: `+15005550006` always ends `delivered`
  and no phone gets a text.
- Errors are JSON: `{"error": {"code", "message", "param"}}` with a 4xx status.
  On `429`, wait `Retry-After` seconds and retry.
- Send only from server code that runs after a real event (a signup, an order).
  Never expose an endpoint that texts any number a visitor types.

export TEXTKIT_API_KEY=ssms_sk_test_...

bun add jointextkit

import { TextKit } from 'jointextkit';

const sms = new TextKit(); // reads TEXTKIT_API_KEY

const message = await sms.messages.send({
  to: '+15005550006',
  body: 'Hello from TextKit',
});

console.log(message.id, message.status);

bun send.ts

import { TextKit, TextKitError } from 'jointextkit';

try {
  await sms.messages.send({ to: '+15005550006', body: 'Hello from TextKit' });
} catch (err) {
  if (err instanceof TextKitError) {
    // err.code: 'invalid_request', 'rate_limited', ...  err.status: the HTTP status
    console.error(err.status, err.code, err.message);
  } else {
    throw err;
  }
}