Add restart: unless-stopped to all docker-compose services

Root cause of the 502: the host's disk filled up (down to ~511MB
free), which appears to have restarted the Docker daemon. Every other
service on this shared host came back up automatically (they all have
restart policies); guideCity's three containers didn't and stayed
down. Freed ~3.2GB via `docker builder prune` + `docker image prune`
(safe: build cache and dangling images only, no running containers
touched) and brought the stack back up.

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

docker-compose.yml

@@ -1,6 +1,7 @@
 services:
   db:
     image: postgis/postgis:16-3.4
+    restart: unless-stopped
     environment:
       POSTGRES_USER: ${POSTGRES_USER}
       POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
@@ -17,6 +18,7 @@ services:
 
   api:
     build: ./backend
+    restart: unless-stopped
     environment:
       DATABASE_URL: postgresql+psycopg://${POSTGRES_USER}:${POSTGRES_PASSWORD}@db:5432/${POSTGRES_DB}
       LOG_LEVEL: ${LOG_LEVEL:-INFO}
@@ -31,6 +33,7 @@ services:
 
   adminer:
     image: adminer
+    restart: unless-stopped
     ports:
       - "8080:8080"
     depends_on: