fix: update Prisma schema path and upgrade PostgreSQL image to 18-alpine

SPEC.md

@@ -18,7 +18,7 @@
 ```
 ./backend/             # Node backend (rj-web)
 ./frontend/            # React + Vite frontend
-./prisma/schema.prisma # Prisma schema
+./backend/prisma/schema.prisma # Prisma schema
 ./docker-compose.yml   # Compose + Dockerfile for PP itself
 ```
 

docker-compose.yml

@@ -2,7 +2,7 @@ version: "3.9"
 
 services:
   pp-db:
-    image: postgres:16-alpine
+    image: postgres:18-alpine
     restart: unless-stopped
     environment:
       POSTGRES_USER: pp
@@ -15,8 +15,6 @@ services:
       interval: 10s
       timeout: 5s
       retries: 5
-    ports:
-      - "5432:5432"
 
   pp-backend:
     build: