chore(deps): update postgres docker tag to v18

compose.yml

@@ -3,7 +3,7 @@ version: "3.8"
 
 services:
   app:
-    image: "pretix/standalone:2026.7.0"
+    image: "pretix/standalone:2026.5.1"
     networks:
       - proxy
       - internal
@@ -31,7 +31,7 @@ services:
         - "traefik.http.routers.${STACK_NAME}.rule=Host(`${DOMAIN}`${EXTRA_DOMAINS})"
         - "traefik.http.routers.${STACK_NAME}.entrypoints=web-secure"
         - "traefik.http.routers.${STACK_NAME}.tls.certresolver=${LETS_ENCRYPT_ENV}"
-        - "coop-cloud.${STACK_NAME}.version=2.8.0+2026.7.0"
+        - "coop-cloud.${STACK_NAME}.version=2.7.0+2026.5.1"
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost/healthcheck"]
       interval: 30s
@@ -40,7 +40,7 @@ services:
       start_period: 5m
 
   db:
-    image: postgres:16
+    image: postgres:18
     volumes:
       - "postgres:/var/lib/postgresql/data"
     networks:
@@ -77,7 +77,7 @@ services:
         backupbot.restore.post-hook: "/pg_backup.sh restore"
 
   redis:
-    image: redis:8.10.1-alpine
+    image: redis:8.8.0-alpine
     volumes:
       - "redis:/data"
     healthcheck: