fix(docker): add --legacy-peer-deps to npm ci for svelte-markdown@0.4.1 compat

svelte-markdown@0.4.1 declares peer dependency svelte@^4.0.0, but the
project uses svelte@^5.43.8. In clean Docker builds, npm ci strictly
validates peer deps and fails. Adding --legacy-peer-deps works around
the incompatibility until svelte-markdown supports Svelte 5.

docker-compose.e2e.yml

@@ -69,7 +69,7 @@ services:
       - /tmp/playwright-report:/workspace/frontend/playwright-report
     command: >
       sh -c "
-        npm ci &&
+        npm ci --legacy-peer-deps &&
         npx playwright install chromium &&
         npx playwright test
       "