#3709 feat(examples): add Mailtrap example

Adds a Mailtrap example under examples/, following the same shape as the existing Brevo (#3704) and Plunk examples. It renders the email with react-email and sends it through the official mailtrap SDK's send() method. I checked the payload against the SDK's TypeScript types (mailtrap@4.9.0); it typechecks clean and builds with tsdown.

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Summary by cubic

Adds a Mailtrap example under examples/mailtrap that renders an email with react-email and sends it using the official mailtrap SDK. It’s a minimal reference integration and does not modify production code.

• New example package react-email-with-mailtrap builds with tsdown (ESM, Node 20) and typechecks against mailtrap@4.9.0.
• Requires MAILTRAP_TOKEN; the example uses MailtrapClient.send() with HTML rendered via react-email.
• Updates pnpm-lock.yaml for the new example dependencies and applies linting; no behavior changes.