perf(web): pin /home/* assets to 1y immutable cache

Next.js serves /public files with `Cache-Control: public, max-age=0,
must-revalidate`, so the home covers + first-act JSON were re-fetched on
every visit. Verified against 30 days of Vercel metrics: /home/* alone was
~62% of Fast Data Transfer egress (5.42 GB) while the files total only
~31 MB — the same bytes re-downloaded hundreds of times.

Add a headers() rule scoping `public, max-age=31536000, immutable` to
/home/:path* only; other paths keep their defaults (verified /icon.svg
still returns no-cache). Filenames under /home are stable (covers fN/mN.webp,
first-act JSON by card name), so immutable is safe; if a first-act JSON is
ever re-baked under the same name, bump a query string or purge the cache.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

next.config.ts

@@ -6,6 +6,17 @@ const config: NextConfig = {
   turbopack: {
     root: __dirname,
   },
+  // /public defaults to `max-age=0, must-revalidate`; pin the stable /home/* covers + first-act JSON for 1y so browsers/CDN stop re-downloading them.
+  async headers() {
+    return [
+      {
+        source: "/home/:path*",
+        headers: [
+          { key: "Cache-Control", value: "public, max-age=31536000, immutable" },
+        ],
+      },
+    ];
+  },
 };
 
 export default config;