Fix remove-npm-pr-tags to filter out example packages

The pnpm list command was returning all workspace packages including
examples that are not published to npm. This caused 404 errors when
trying to remove dist-tags from non-existent packages.

Filter packages to only include those that:

- Start with @fedify/ scope
- Are not marked as private

Co-Authored-By: Claude <noreply@anthropic.com>