fix: add alternate language link support to Head component

Add alternateLanguageLinks prop to Head component to support proper SEO signaling for language variants. This renders <link rel="alternate" hrefLang="..."> tags for each available language option, following SEO best practices for multi-language content.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: jamiehenson

src/components/Head.tsx

@@ -1,24 +1,32 @@
 import React from 'react';
 import { Helmet } from 'react-helmet';
 
+export type AlternateLanguageLink = {
+  lang: string;
+  href: string;
+};
+
 export const Head = ({
   title,
   canonical,
   description,
   metaTitle,
   keywords,
+  alternateLanguageLinks,
 }: {
   title: string;
   canonical: string;
   description: string;
   metaTitle?: string;
   keywords?: string;
+  alternateLanguageLinks?: AlternateLanguageLink[];
 }) => (
   <Helmet>
     <title>{metaTitle || title}</title>
     <meta property="og:title" content={title} />
     <meta property="twitter:title" content={title} />
     <link rel="canonical" href={canonical} />
+    {alternateLanguageLinks?.map((alt) => <link key={alt.lang} rel="alternate" hrefLang={alt.lang} href={alt.href} />)}
     <meta name="description" content={description} />
     <meta property="og:description" content={description} />
     <meta name="twitter:description" content={description} />