Add PWA support with manifest, service worker, and icons

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/next.config.js

@@ -1,7 +1,24 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
   reactStrictMode: true,
-  output: 'standalone'
+  output: 'standalone',
+  async headers() {
+    return [
+      {
+        source: '/sw.js',
+        headers: [
+          {
+            key: 'Cache-Control',
+            value: 'public, max-age=0, must-revalidate',
+          },
+          {
+            key: 'Service-Worker-Allowed',
+            value: '/',
+          },
+        ],
+      },
+    ];
+  },
 };
 
 module.exports = nextConfig;