Initial commit: split single-file PWA into index.html, styles.css, app.js, sw.js

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

sw.js

@@ -0,0 +1,32 @@
+const CACHE = 'ns-v12';
+const PRECACHE = ['/', 'index.html', 'styles.css', 'app.js', 'sw.js'];
+const SKIP_URLS = ['/rest/stream', '/rest/download'];
+
+self.addEventListener('install', e => {
+  e.waitUntil(caches.open(CACHE).then(c => c.addAll(PRECACHE)));
+  self.skipWaiting();
+});
+
+self.addEventListener('activate', e => {
+  e.waitUntil(
+    caches.keys().then(keys =>
+      Promise.all(keys.filter(k => k !== CACHE).map(k => caches.delete(k)))
+    )
+  );
+  self.clients.claim();
+});
+
+self.addEventListener('fetch', e => {
+  if (SKIP_URLS.some(u => e.request.url.includes(u))) return;
+  e.respondWith(
+    caches.match(e.request).then(cached =>
+      cached || fetch(e.request).then(res => {
+        if (res.status === 200 && e.request.method === 'GET') {
+          const clone = res.clone();
+          caches.open(CACHE).then(c => c.put(e.request, clone));
+        }
+        return res;
+      }).catch(() => cached)
+    )
+  );
+});