Add Email Notification Service with Templating

[Mkalbani]

Description

Integrate an email notification service that sends transactional emails for key game events — welcome on registration, password reset, achievement unlocked, weekly score summary. Emails should be templated, branded, and delivered via a configurable SMTP provider or third-party service like SendGrid. The service should queue emails asynchronously to avoid blocking API responses.

Acceptance Criteria

• An email module is scaffolded at src/email/
• Templates exist for: welcome, password-reset, achievement-unlocked, and weekly-summary
• Emails are queued via a Bull/BullMQ job queue and sent asynchronously
• Provider (SMTP or SendGrid) is selected and configured via environment variables
• Failed sends are retried up to 3 times with exponential backoff
• POST /admin/email/test (admin-only) sends a test email to a specified address
• Players can opt out of non-critical emails via PATCH /users/me/email-preferences
• Unit tests cover template rendering, queue submission, retry logic, and opt-out enforcement

[Ayinkx]

Hi l would like to take this job

[Fabluchy]

I’m interested in contributing to this task because I enjoy building reliable backend features that improve user experience and system communication. I have experience working with technical projects, data analysis, SQL, and understanding application workflows, which has strengthened my problem-solving and attention to detail. I’m comfortable working with existing codebases, implementing structured solutions, and ensuring features are maintainable and easy to extend. I’d like to contribute by developing an email notification service with reusable templates and helping create a more efficient communication system.

[grantfox-oss]

🦊 GrantFox — @Fabluchy has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #81)
2. Your PR will be reviewed by the MindFlowInteractive maintainers

Good luck! Track your progress on GrantFox.