[BACKEND] Email setup

[aleckshen]

Is your feature request related to a problem? Please describe

The app has no email provider configured, so transactional emails (registration confirmations, password resets) cannot be sent.

Describe the solution you'd like

Set up Resend as the email provider using the official Payload plugin.

Steps:

1. Install @payloadcms/email-resend
2. Add resendAdapter to payload.config.ts with defaultFromAddress: 'onboarding@resend.dev (changed to uoavc email later) and defaultFromName: 'UOAVC'
3. Add RESEND_API_KEY to .env (with the real key) and .env.example (blank, with a comment pointing to https://resend.com)

Describe alternatives you've considered

Other providers (SendGrid, Nodemailer, etc.) were considered but Resend has a first-party Payload adapter and a generous free tier (100 emails/day), making it the simplest option.

Additional context

Resend account and API key required before this can be tested end-to-end. Verify by triggering the "Forgot Password" flow in the admin panel and confirming the email arrives.

Ref: https://payloadcms.com/docs/email/resend

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