feat(docs): wire CodeBlock into MDX components map

All <pre> elements in docs MDX now render through CodeBlock,
which selects one of three modes based on language and title.
CSS styling for each mode follows.

docs/app/docs/[[...slug]]/page.tsx

@@ -0,0 +1,47 @@
+import { source } from "@/lib/source";
+import {
+  DocsPage,
+  DocsBody,
+  DocsTitle,
+  DocsDescription,
+} from "fumadocs-ui/page";
+import { notFound } from "next/navigation";
+import defaultMdxComponents from "fumadocs-ui/mdx";
+import { CodeBlock } from "@/components/code-block";
+
+export default async function Page(props: {
+  params: Promise<{ slug?: string[] }>;
+}) {
+  const params = await props.params;
+  const page = source.getPage(params.slug);
+  if (!page) notFound();
+
+  const MDX = page.data.body;
+
+  return (
+    <DocsPage toc={page.data.toc}>
+      <DocsTitle>{page.data.title}</DocsTitle>
+      <DocsDescription>{page.data.description}</DocsDescription>
+      <DocsBody>
+        <MDX components={{ ...defaultMdxComponents, pre: CodeBlock }} />
+      </DocsBody>
+    </DocsPage>
+  );
+}
+
+export function generateStaticParams() {
+  return source.generateParams();
+}
+
+export async function generateMetadata(props: {
+  params: Promise<{ slug?: string[] }>;
+}) {
+  const params = await props.params;
+  const page = source.getPage(params.slug);
+  if (!page) notFound();
+
+  return {
+    title: page.data.title,
+    description: page.data.description,
+  };
+}