Sync dev compose with Hetzner hot-standby: postgres 18, loopback port, versioned volume

Change was made live on the build server on 20260701 and is now captured
in git per the no-drift rule.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docker-compose.yml

@@ -1,15 +1,15 @@
 services:
   db:
-    image: postgres:16-alpine
+    image: postgres:18-alpine
     restart: unless-stopped
     environment:
       POSTGRES_USER: lms_user
       POSTGRES_PASSWORD: lms_password
       POSTGRES_DB: lms_db
     ports:
-      - "5432:5432"
+      - "127.0.0.1:5432:5432"
     volumes:
-      - postgres_data:/var/lib/postgresql/data
+      - postgres_data:/var/lib/postgresql
 
 volumes:
   postgres_data: