fix(mail): Copy SSH keys into Docker image instead of volume mount

Remove volume mount for SSH keys and rely on Dockerfile COPY instruction
to bake SSH keys into the image during build. This ensures proper
permissions and ownership for the django user.

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

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

smoothschedule/docker-compose.production.yml

@@ -18,8 +18,6 @@ services:
     env_file:
       - ./.envs/.production/.django
       - ./.envs/.production/.postgres
-    volumes:
-      - ./.ssh:/app/.ssh:ro
     command: /start
 
   postgres: