Add PWA support with manifest, service worker, and icons

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

frontend/src/components/sw-registrar.tsx

@@ -0,0 +1,15 @@
+"use client";
+
+import { useEffect } from "react";
+
+export function ServiceWorkerRegistrar() {
+  useEffect(() => {
+    if ("serviceWorker" in navigator && process.env.NODE_ENV === "production") {
+      navigator.serviceWorker.register("/sw.js").catch((err) => {
+        console.warn("SW registration failed:", err);
+      });
+    }
+  }, []);
+
+  return null;
+}