Add Cloudflare deployment for docs site

[hudsonaikins]

Summary

• add OpenNext Cloudflare deployment config for the Fumadocs site
• add docs Worker config, R2 incremental cache binding, and static asset cache headers
• add docs deploy/preview scripts through Wrangler and @opennextjs/cloudflare

Deployed proof

• Docs: https://agent-permit-docs.hudson-228.workers.dev/docs
• Dashboard: https://agent-permit-dashboard.pages.dev
• API: https://agent-permit-worker.hudson-228.workers.dev/api/health

Checks

• cd docs-site && bun run build
• uv run pytest -q
• python3 tools/release_check.py

Notes

• Cloudflare R2 bucket agent-permit-docs-opennext-cache already existed in the account and is used by the docs Worker for OpenNext incremental cache.
• Local .dev.vars remains ignored and was not committed.