Run E2E tests against production build in CI

In CI, Playwright now starts apps with production commands (react-router-
serve, node --experimental-strip-types) instead of dev servers. This
catches runtime issues like missing exports and import resolution errors
before deploy. Locally, dev servers are still used for fast iteration.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -175,6 +175,9 @@ jobs:
         if: steps.playwright-cache.outputs.cache-hit == 'true'
         run: pnpm exec playwright install-deps chromium
 
+      - name: Build for production
+        run: pnpm build
+
       - name: Run E2E tests
         run: pnpm test:e2e
         env: