fix(issues): paginate team member lookup

[ruby-automation]

Summary

• Route the team-scoped user action through the existing cursor-paginated reader.
• Normalize member HTTP errors so the CLI authentication and API handlers receive the expected Ash error value.
• Add regression coverage for later-page assignment and assignee filtering, 401/5xx handling, and update the Ash domain ERD.

Verification

• mise exec -- mix ci
• Focused user, mutation, and profile-default tests: 133 passed
• git diff --check

Linear issue: https://linear.app/the-rubyists/issue/EXT-75/paginate-team-scoped-assignee-lookup-and-normalize-member-lookup