Show all imported authors by default in metadata form

[beanbean9339]

Problem

When the GitHub importer supplies more than three authors, the metadata form initially hides the rest. Users reviewing imported metadata may overlook names even when the import succeeded.

Scope

Make the author list expanded by default while preserving the existing collapse/expand interaction. This is a form presentation change, separate from contributor selection and issue #56.

Acceptance criteria

• All imported authors are visible on initial render.
• Existing show fewer/show all control still works.
• No change to the contributor importer or author ordering.