chore(docker): restart backend, frontend, and nginx unless stopped

Matches postgres, which already had restart: unless-stopped — the app
containers were the only ones that didn't come back automatically
after a host reboot or Docker Desktop restart.

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

docker-compose.yml

@@ -2,6 +2,7 @@ services:
   backend:
     build: ./backend
     container_name: bellsystems-backend
+    restart: unless-stopped
     env_file: .env
     volumes:
       - ./backend:/app
@@ -22,12 +23,14 @@ services:
   frontend:
     build: ./frontend
     container_name: bellsystems-frontend
+    restart: unless-stopped
     networks:
       - internal
 
   nginx:
     image: nginx:alpine
     container_name: bellsystems-nginx
+    restart: unless-stopped
     ports:
       - "90:80"     # access v2 on localhost:8001
     volumes: