Scalable Email Infrastructure for CDLI Framework

The CDLI framework currently sends transactional emails synchronously during web requests, coupling application performance directly to SMTP availability. This project redesigns the email system into a reliable, background-driven pipeline by moving email delivery into asynchronous jobs processed by a dedicated worker. The work builds on the existing Redis and Postfix infrastructure already present in the repository, adding persistent job storage, retry logic, failure tracking, an admin monitoring dashboard, rate limiting, and a shared email template system — making email a first-class, observable part of the application rather than a side effect of user actions.