Replace Mailhog with Mailpit for local dev email testing

[scanner]

Summary

Replace Mailhog with Mailpit in the local development Docker Compose stack. Mailhog is unmaintained and does not support TLS/SSL or SMTP authentication — the original reason GH-61 was opened. Mailpit is its actively-maintained successor and supports TLS, SMTP authentication, and everything Mailhog did.

Closes #61.

Current Setup

Location	Current value
docker-compose.yml	image: druidfi/mailhog:1.0.1 on port 8025
.env	EMAIL_HOST=mailhog
settings.py	EMAIL_HOST = env("EMAIL_HOST", default="mailhog")
Makefile	logs target tails mailhog container

Changes Required

• docker-compose.yml: replace mailhog service with mailpit (axllent/mailpit); configure TLS and SMTP auth; expose web UI port (default 8025) and SMTP port
• .env: update EMAIL_HOST=mailhog → EMAIL_HOST=mailpit
• settings.py: update default="mailhog" → default="mailpit"
• Makefile: update logs target to reference mailpit
• SSL certs: Mailpit can use the existing mkcert-generated certs from ssl/ for its TLS listener
• SMTP auth: configure Mailpit with credentials matching whatever the dev SMTP settings expect

References

• Mailpit repo: https://github.com/axllent/mailpit
• Mailpit docs on TLS: https://mailpit.axllent.org/docs/configuration/tls/
• Mailpit docs on SMTP auth: https://mailpit.axllent.org/docs/configuration/smtp-authentication/