Add meta descriptions to component pages

[minimaldesign]

The components collection schema (src/content.config.ts) has no description field, so all 24 component pages fall back to the same default meta description in BaseLayout.astro ("The CSS framework for CSS lovers."). Search engines see duplicate descriptions across the whole /components section.

Suggested fix:

1. Add an optional description field to the components schema (same as the docs collection).
2. Write a one-line description per component (also improves /llms.txt, which already prints descriptions for docs entries but not components).
3. Consider making description required once all files have one.

Found in the pre-v1 audit.