Clarify preview feedback path on contribution docs

[DicksonWu654]

Closes #59

Summary

• clarify the lightweight feedback path for contributors reviewing an existing PR
• explain that the rendered preview is the Cloudflare Pages preview linked from the PR
• explain that proofreading or feedback should be left on the PR itself, without opening a separate PR
• update both the docs page and the synced root CONTRIBUTING file

Verification

• pnpm exec markdownlint-cli2 docs/pages/contribute/contributing.mdx
• node utils/sync-contributing.js
• Claude CLI review of the final diff

[github-actions]

built with Refined Cloudflare Pages Action

⚡ Cloudflare Pages Deployment

Name	Status	Preview	Last Commit
frameworks	✅ Ready (View Log)	Visit Preview	d9749fb

[DicksonWu654]

Clarified the intent here in the contribution docs.

This issue is about contributor workflow, not a new site feature: the Cloudflare Pages link on a PR is only a rendered preview for review, and feedback should stay on the existing PR rather than opening a separate PR or expecting comments directly on the live site.

I updated both docs/pages/contribute/contributing.mdx and the synced root CONTRIBUTING.md to make that explicit.

[DicksonWu654]

lgtm

[DicksonWu654]

@mattaereal I'm not 100% if I've addressed the original issue #59 - so feel free to edit / just close this issue if it doesn't