Fix: Remove PostgreSQL port mapping in production

Database is only accessed via Docker network, not externally.
This prevents port 5432 conflicts on production servers.

docker-compose.prod.yml

@@ -13,8 +13,9 @@ services:
       - postgres_data:/var/lib/postgresql/data
       # Mount all migration files for initialization
       - ./migrations:/docker-entrypoint-initdb.d:ro
-    ports:
-      - "${POSTGRES_PORT:-5432}:5432"
+    # NO external port mapping - only accessible via Docker network
+    # ports:
+    #   - "${POSTGRES_PORT:-5432}:5432"
     restart: always
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER}"]