fix: remove unused Coolify mail env vars, use database config

Coolify stores SMTP settings in the database (instance_settings table)
rather than reading from environment variables.

SMTP settings configured directly in database:
- smtp_enabled: true
- smtp_host: net_mailpit
- smtp_port: 1025
- smtp_from_address: hi@pivoine.art
- smtp_from_name: Coolify

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

dev/compose.yaml

@@ -126,15 +126,6 @@ services:
       - PUSHER_APP_SECRET=${DEV_COOLIFY_PUSHER_APP_SECRET}
       - PUSHER_SCHEME=https
       - SSL_MODE=off
-      # Mail configuration
-      - MAIL_MAILER=smtp
-      - MAIL_HOST=net_mailpit
-      - MAIL_PORT=1025
-      - MAIL_ENCRYPTION=
-      - MAIL_USERNAME=
-      - MAIL_PASSWORD=
-      - MAIL_FROM_ADDRESS=${EMAIL_FROM}
-      - MAIL_FROM_NAME=Coolify
     networks:
       - compose_network
     labels: