Fix Dockerfile shell operator precedence bug causing build failures

The e2e test command had incorrect operator precedence:
  npm run test:e2e || echo "..." && touch marker

This was parsed as:
  npm run test:e2e || (echo "..." && touch marker)

Which meant:
- If e2e tests PASS → touch never runs → marker file missing → build fails ❌
- If e2e tests FAIL → touch runs → marker file exists → build succeeds ✓

This was backwards\! The production stage expects the marker file at line 64:
  COPY --from=e2e-test /app/.e2e-tests-passed /tmp/.e2e-tests-passed

Fixed by adding parentheses to ensure correct precedence:
  (npm run test:e2e || echo "...") && touch marker

Now the marker file is always created regardless of test outcome,
which is the intended behavior for a non-blocking test stage.

This fixes the docker-build-test CI failures that occurred after the
e2e tests started passing. The build was failing because tests were
passing but the marker file wasn't being created.

https://claude.ai/code/session_7d4f1b7d-7a0d-44db-b437-c76b6b61dfb2

frontend/Dockerfile

@@ -52,7 +52,7 @@ COPY . .
 RUN npm run build
 
 # Run e2e tests (non-blocking in CI as requires running backend)
-RUN npm run test:e2e || echo "E2E tests skipped (requires running services)" && touch /app/.e2e-tests-passed
+RUN (npm run test:e2e || echo "E2E tests skipped (requires running services)") && touch /app/.e2e-tests-passed
 
 # Production stage
 FROM node:20-slim AS production