chore: Remove SSL cert handling - use external reverse proxy

- Nginx now listens on HTTP only (port 80)
- Remove SSL cert volume mounts from docker-compose
- Remove SSL troubleshooting sections
- Update docs to indicate SSL handled by Caddy/reverse proxy
- Simplify nginx.conf to remove HTTPS server block

docker-compose.yml

@@ -96,10 +96,8 @@ services:
     container_name: coop-nginx
     ports:
       - "80:80"
-      - "443:443"
     volumes:
       - ./docker/nginx/nginx.conf:/etc/nginx/nginx.conf:ro
-      - ./docker/nginx/ssl:/etc/nginx/ssl:ro
     depends_on:
       frontend:
         condition: service_started