[Workers] Improve module registry documentation

[irvinebroque]

Summary

Builds on cloudflare#32550 by making the new module registry documentation more actionable and discoverable.

• Prioritizes import.meta, dynamic imports, and cold-start behavior in the changelog, with code examples.
• Adds module-loading guidance to the Workers Web standards and Node.js compatibility pages.
• Expands the reference with MDN context, bundling caveats, and cross-links to related Workers documentation.

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.

[github-actions]

Hey there, we've marked this pull request as stale because there's no recent activity on it. This label helps us identify PRs that might need updates (or to be closed out by our team if no longer relevant).

[github-actions]

Hey there, we've closed out this pull request because it's been stale for a while and there's been no additional action on it. If these changes are still relevant, open a new pull request (or flag to us in a GitHub issue).