Pin image digests and disable TRACE method in nginx

- nginx and mysql images pinned to SHA256 digests
- nginx: return 405 on TRACE requests

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

docker-compose.yml

@@ -1,6 +1,6 @@
 services:
   nginx:
-    image: nginx:alpine
+    image: nginx:alpine@sha256:4001b8091adb507866f42c251759b40290995629415d46684a32d3ede850c976
     ports:
       - "8057:80"
     volumes:
@@ -37,7 +37,7 @@ services:
       start_period: 30s
 
   db:
-    image: mysql:8
+    image: mysql:8@sha256:c36050afdca850f23cef85703f84c7531a5ae155a11b5ee1c60acb09937c4084
     environment:
       - MYSQL_ROOT_PASSWORD=${MYSQL_ROOT_PASSWORD}
       - MYSQL_DATABASE=${MYSQL_DATABASE}