Fix y-websocket v2 server startup in hardened container

Use node directly instead of npx which fails with
"Permission denied" when cap_drop: ALL is set.

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

docker-compose.yml

@@ -57,7 +57,7 @@ services:
       - -c
       - |
         npm install @y/websocket-server > /dev/null 2>&1
-        npx y-websocket
+        node node_modules/@y/websocket-server/src/server.js
     environment:
       - HOST=0.0.0.0
       - PORT=1234