Move functionality and style of Concepts and Vocabulary into specific components

Context

I have moved the components/vocabulary/VocabularyEntry.astro component to components/reference/VocabularyEntry.astro.
(Let's make sure that doesn't blow up anything.)

Objective:

Move the functionality and style of both Concepts and Vocabulary currently insite/src/pages/more-about/index.astro
into two components:
  1. components/reference/ConceptPreviewCard.astro
  2. components/reference/VocabularyPreviewCard.astro
into the @components/reference directory.