chore: switch nginx to HTTP-only for Cloudflare Flexible SSL

Cloudflare terminates TLS at the edge; origin only needs port 80.
Removes SSL cert requirement, drops port 443 from compose.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -53,11 +53,9 @@ services:
     image: nginx:alpine
     restart: unless-stopped
     ports:
-      - "${HOST_PORT:-443}:443"
       - "80:80"
     volumes:
       - ./nginx/nginx.conf:/etc/nginx/nginx.conf:ro
-      - ./nginx/ssl:/etc/nginx/ssl:ro
     depends_on:
       - backend
       - frontend