Fix PWA installation support

public/sw.js

@@ -1,10 +1,17 @@
-const CACHE = "cet6-shell-v1";
-const APP_SHELL = ["/", "/tasks", "/stats", "/review", "/manifest.webmanifest", "/favicon.svg"];
+const CACHE = "cet6-shell-v2";
+const APP_SHELL = ["/", "/manifest.webmanifest", "/favicon.svg", "/icon-192.png", "/icon-512.png"];
 self.addEventListener("install", event => event.waitUntil(caches.open(CACHE).then(cache => cache.addAll(APP_SHELL)).then(() => self.skipWaiting())));
-self.addEventListener("activate", event => event.waitUntil(self.clients.claim()));
+self.addEventListener("activate", event => event.waitUntil(
+  caches.keys().then(keys => Promise.all(keys.filter(key => key !== CACHE).map(key => caches.delete(key)))).then(() => self.clients.claim())
+));
 self.addEventListener("fetch", event => {
   const request = event.request;
   if (request.method !== "GET" || new URL(request.url).origin !== location.origin) return;
   if (request.url.includes("/api/")) return;
-  event.respondWith(fetch(request).then(response => { const copy = response.clone(); caches.open(CACHE).then(cache => cache.put(request, copy)); return response; }).catch(() => caches.match(request).then(found => found || caches.match("/"))));
+  event.respondWith(fetch(request).then(response => {
+    if (response.ok && new URL(request.url).pathname.startsWith("/_next/")) {
+      const copy = response.clone(); caches.open(CACHE).then(cache => cache.put(request, copy));
+    }
+    return response;
+  }).catch(() => caches.match(request).then(found => found || caches.match("/"))));
 });