Remove unused RichText import from bluesky.ts to fix CI lint failure (#1347)

The RichText import from @atproto/api was unused after refactoring the
Bluesky posting logic to use manual facets instead of RichText helpers.
This caused the ESLint no-unused-vars rule to fail in CI.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: captbaritone