fix(docker): add @playwright/test to server devDependencies

The Dockerfile's playwright install step requires the binary in
node_modules/.bin/, but playwright was only a UI dependency. This adds
@playwright/test to server devDependencies so the Docker build can
successfully run `./node_modules/.bin/playwright install chromium`.

Fixes the "playwright: not found" error during Docker image build.

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

apps/server/package.json

@@ -45,6 +45,7 @@
     "yaml": "2.7.0"
   },
   "devDependencies": {
+    "@playwright/test": "1.57.0",
     "@types/cookie": "0.6.0",
     "@types/cookie-parser": "1.4.10",
     "@types/cors": "2.8.19",