Revert "Add subdomain for staging (#989)"

[avivkeller]

This reverts commit fd85777.

[cursor]

PR Summary

Low Risk
Staging-only Wrangler routing revert; production routes and worker logic are untouched.

Overview
Reverts the staging r2.staging.nodejs.org Cloudflare route from wrangler.jsonc so the staging worker is no longer bound to that hostname pattern.

Staging workers_dev is set inside vars (with workers_dev: true at the env level removed), matching the layout before the subdomain change. Production routes are unchanged.

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