Astro 7 mdx() remarkPlugins silently ignored — use markdown.processor unified()

In Astro 7, passing remarkPlugins directly to the mdx() integration (e.g. mdx({ remarkPlugins: [...] })) is deprecated AND silently broken: Astro 7's new default markdown processor 'Sätteri' replaces unified, and @astrojs/mdx's isSatteriProcessor code path only forwards gfm/smartypants from processor.options.features — not remarkPlugins/rehypePlugins/remarkRehype. Trap: it looks safe because .mdx files use their own unified/@mdx-js pipeline (unaffected by Sätteri, which only changes plain .md handling), so the plugin appears correctly wired but simply never executes — causing silent data loss (e.g. data.astro.frontmatter.X never populated, no error thrown). Fix: install @astrojs/markdown-remark explicitly as a direct dependency and configure markdown: { processor: unified({ remarkPlugins: [...] }) } at the top level of astro.config instead of via the mdx() integration options.