feat: restore front-page VSCode carousel

[magnus-madsen]

Summary

The Astro rewrite (#165) left the front-page VSCode carousel as inert Bootstrap markup showing only one static image, with a TODO to find a carousel replacement. This PR restores it:

• Adds a small Carousel.astro component that renders Bootstrap 4 carousel markup (slides, indicators, prev/next controls) from an items prop.
• Since the site only loads Bootstrap's CSS (no jQuery/Bootstrap JS), a ~40-line inline script performs Bootstrap's class-swap dance to animate transitions, with a timeout fallback for prefers-reduced-motion where transitionend never fires.
• Restores all four slides with their original captions from the pre-rewrite Home.jsx: Semantic Highlighting, Hover to Inspect, Highlight References, Inline Errors.
• No new dependencies.

Test plan

• npm run build succeeds; built HTML contains all four slides, indicators, and controls.
• Verified manually via npm run preview: arrows slide between screenshots with animation and wrap around, indicators jump to and track the current slide, captions display.

🤖 Generated with Claude Code