fix: Update postgres service configuration in compose.yml for clarity and correctness

postgres/compose.yml

@@ -1,8 +1,7 @@
 services:
   postgres:
-    build:
-      context: .
-      dockerfile: Dockerfile
+    # run `just build postgres` first
+    build: database-postgres:latest
     restart: unless-stopped
     environment:
       POSTGRES_USER: ${POSTGRES_USER:-postgres}
@@ -11,7 +10,7 @@ services:
     ports:
       - "${POSTGRES_PORT:-5432}:5432"
     volumes:
-      - postgres_data:/var/lib/postgresql/data
+      - postgres_data:/var/lib/postgresql
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-postgres}"]
       interval: 10s