fix: configure Mailpit relay via environment variables

- Remove mailpit-relay.yaml file (env vars not substituted in mounts)
- Use MP_SMTP_RELAY_* environment variables directly
- Fixes crash loop due to missing relay host configuration

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

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

net/compose.yaml

@@ -234,11 +234,15 @@ services:
       MP_SMTP_AUTH_ACCEPT_ANY: 1
       MP_SMTP_AUTH_ALLOW_INSECURE: 1
       MP_MAX_MESSAGES: 5000
-      # SMTP relay to IONOS
-      MP_SMTP_RELAY_CONFIG: /config/relay.yaml
+      # SMTP relay to IONOS via environment variables
+      MP_SMTP_RELAY_HOST: ${EMAIL_SMTP_HOST}
+      MP_SMTP_RELAY_PORT: ${EMAIL_SMTP_PORT}
+      MP_SMTP_RELAY_USER: ${EMAIL_SMTP_USER}
+      MP_SMTP_RELAY_PASS: ${EMAIL_SMTP_PASSWORD}
+      MP_SMTP_RELAY_AUTH: plain
+      MP_SMTP_RELAY_STARTTLS: "true"
     volumes:
       - mailpit_data:/data
-      - ./mailpit-relay.yaml:/config/relay.yaml:ro
     networks:
       - compose_network
     labels:

net/mailpit-relay.yaml

@@ -1,11 +0,0 @@
-# Mailpit SMTP Relay Configuration
-# Relays all outbound emails through IONOS SMTP
-
-# Default relay for all emails
-relay:
-  host: ${EMAIL_SMTP_HOST}
-  port: ${EMAIL_SMTP_PORT}
-  username: ${EMAIL_SMTP_USER}
-  password: ${EMAIL_SMTP_PASSWORD}
-  starttls: true
-  auth: plain