fix: Bind PostgreSQL port to 127.0.0.1:5432:5432 for localhost-only access

- Changed PostgreSQL service port binding from 5432:5432 to 127.0.0.1:5432:5432 in docker-compose.yml
- This restricts PostgreSQL to listen only on localhost, improving security by preventing access from other interfaces
- Marked task 1.6 as completed

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

docker-compose.yml

@@ -66,7 +66,7 @@ services:
   postgres:
     image: postgres:16-alpine
     ports:
-      - "5432:5432"
+      - "127.0.0.1:5432:5432"
     volumes:
       - postgres-data:/var/lib/postgresql/data
     environment: