Fix plugin frontend-tests template: use dev mode not prod (#7402)

Prod mode enables rate limiting which causes frontend tests to fail
silently. Dev mode disables rate limiting for testing.

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

bin/plugins/lib/frontend-tests.yml

@@ -78,7 +78,7 @@ jobs:
       - name: Run the frontend tests
         shell: bash
         run: |
-          pnpm run prod &
+          pnpm run dev &
           connected=false
           can_connect() {
           curl -sSfo /dev/null http://localhost:9001/ || return 1