Fix MDX internal links missing basePath by using Next.js Link component

MDX content links like [text](/docs/...) rendered as plain <a> tags,
which don't get the Next.js basePath prefix, causing 404s on GitHub
Pages. Added MdxLink component that routes internal links through
Next.js Link for automatic basePath handling.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mokuwaki

src/components/docs/mdx/index.tsx

@@ -1,3 +1,4 @@
+import Link from "next/link";
 import { Heading } from "./Heading";
 import { CodeBlock } from "./CodeBlock";
 import { Callout } from "./Callout";
@@ -12,6 +13,14 @@ import { Badge } from "./Badge";
 import { FileTree } from "./FileTree";
 import { Image } from "./Image";
 
+function MdxLink(props: React.AnchorHTMLAttributes<HTMLAnchorElement>) {
+  const { href, children, ...rest } = props;
+  if (href && href.startsWith("/")) {
+    return <Link href={href} {...rest}>{children}</Link>;
+  }
+  return <a href={href} {...rest}>{children}</a>;
+}
+
 export { Accordion, AccordionItem } from "./Accordion";
 export { ApiTable } from "./ApiTable";
 export { Badge } from "./Badge";
@@ -42,6 +51,7 @@ export const mdxComponents: Record<string, React.ComponentType<any>> = {
   table: Table,
   pre: CodeBlock,
   img: Image,
+  a: MdxLink,
   Callout,
   Steps,
   Tabs,