Dashboard: de-emphasize the create-publication button when one exists
The "+ New publication" button was a prominent, sun-filled primary in the
list header in every state. But once a writer has a publication, their wanted
action is to write (already the top-bar CTA), not to create another.
Make the button state-dependent: keep it prominent in the empty state, where
creating a publication is the point, and render it as a quiet secondary
control below the list once at least one publication exists.