Replaced highlight.js with Astro’s built-in Shiki integration for syntax highlighting. This removes the external CDN dependency and gives better highlighting out of the box. Reworked the code block styling to use Shiki’s astro-code classes, including the copy badge and responsive margins.

Added a new remark-warning-block plugin that converts :::warning directives into styled callout blocks, and used it to add deprecation warnings to the refactoring post in the Steering the Vibe series.