In quick-start / worker-vars / email-routing (zh + en), explicitly
call out that a Cloudflare-hosted domain with Email Routing + Catch-all
must be set up before deploying, and that subdomains do not inherit
the parent domain's Email Routing. Closes#1004.
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>