Add infra/docker-compose.yml for shared postgres stack

Move compose config from README into its own file; README now references it.

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

infra/README.md

@@ -26,27 +26,10 @@ Synology NAS
 sudo mkdir -p /volume2/docker/shared/pgdata
 ```
 
-### docker-compose.yml anlegen
+### docker-compose.yml kopieren
 
-Datei `/volume2/docker/shared/docker-compose.yml`:
-
-```yaml
-services:
-  postgres:
-    image: postgres:16-alpine
-    restart: unless-stopped
-    ports:
-      - "5433:5432"
-    environment:
-      POSTGRES_USER: ${POSTGRES_USER:-postgres}
-      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:?POSTGRES_PASSWORD is required}
-    volumes:
-      - /volume2/docker/shared/pgdata:/var/lib/postgresql/data
-    healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-postgres}"]
-      interval: 5s
-      timeout: 5s
-      retries: 5
+```bash
+sudo cp infra/docker-compose.yml /volume2/docker/shared/docker-compose.yml
 ```
 
 ### .env anlegen