Add PWA support with manifest, service worker, and icons

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

frontend/public/sw.js

@@ -0,0 +1,90 @@
+const CACHE_NAME = "notify-v1";
+
+const PRECACHE_URLS = ["/"];
+
+self.addEventListener("install", (event) => {
+  event.waitUntil(
+    caches
+      .open(CACHE_NAME)
+      .then((cache) => cache.addAll(PRECACHE_URLS))
+      .then(() => self.skipWaiting())
+  );
+});
+
+self.addEventListener("activate", (event) => {
+  event.waitUntil(
+    caches
+      .keys()
+      .then((names) =>
+        Promise.all(
+          names
+            .filter((name) => name !== CACHE_NAME)
+            .map((name) => caches.delete(name))
+        )
+      )
+      .then(() => self.clients.claim())
+  );
+});
+
+self.addEventListener("fetch", (event) => {
+  const { request } = event;
+
+  // Skip cross-origin and non-GET requests
+  if (request.method !== "GET" || !request.url.startsWith(self.location.origin)) {
+    return;
+  }
+
+  const url = new URL(request.url);
+
+  // Skip API calls
+  if (url.pathname.startsWith("/api/")) {
+    return;
+  }
+
+  // Next.js static chunks — stale-while-revalidate
+  if (url.pathname.startsWith("/_next/")) {
+    event.respondWith(
+      caches.open(CACHE_NAME).then((cache) =>
+        cache.match(request).then((cached) => {
+          const fetched = fetch(request).then((response) => {
+            if (response.ok) {
+              cache.put(request, response.clone());
+            }
+            return response;
+          });
+          return cached || fetched;
+        })
+      )
+    );
+    return;
+  }
+
+  // Navigation requests — network-first with cache fallback
+  if (request.mode === "navigate") {
+    event.respondWith(
+      fetch(request)
+        .then((response) => {
+          const clone = response.clone();
+          caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
+          return response;
+        })
+        .catch(() => caches.match(request))
+    );
+    return;
+  }
+
+  // Other static assets — cache-first
+  event.respondWith(
+    caches.open(CACHE_NAME).then((cache) =>
+      cache.match(request).then((cached) => {
+        if (cached) return cached;
+        return fetch(request).then((response) => {
+          if (response.ok) {
+            cache.put(request, response.clone());
+          }
+          return response;
+        });
+      })
+    )
+  );
+});