feat: add PWA support (manifest, service worker, icons)

public/sw.js

@@ -0,0 +1,70 @@
+const CACHE = 'klassenportal-v1';
+const PRECACHE = [
+  '/',
+  '/login.html',
+  '/app.html',
+  '/manifest.json',
+  '/favicon.svg',
+  '/icons/icon-192.png',
+  '/icons/icon-512.png',
+  '/icons/apple-touch-icon.png',
+];
+
+self.addEventListener('install', e => {
+  e.waitUntil(
+    caches.open(CACHE)
+      .then(c => c.addAll(PRECACHE))
+      .then(() => self.skipWaiting())
+  );
+});
+
+self.addEventListener('activate', e => {
+  e.waitUntil(
+    caches.keys()
+      .then(keys => Promise.all(
+        keys.filter(k => k !== CACHE).map(k => caches.delete(k))
+      ))
+      .then(() => self.clients.claim())
+  );
+});
+
+self.addEventListener('fetch', e => {
+  const url = new URL(e.request.url);
+
+  // Only handle same-origin GET requests
+  if (url.origin !== self.location.origin) return;
+  if (e.request.method !== 'GET') return;
+
+  // API calls: always network, never cache
+  if (url.pathname.startsWith('/api/')) return;
+
+  // Page navigations: network-first, fallback to cache
+  if (e.request.mode === 'navigate') {
+    e.respondWith(
+      fetch(e.request)
+        .then(r => {
+          const clone = r.clone();
+          caches.open(CACHE).then(c => c.put(e.request, clone));
+          return r;
+        })
+        .catch(() =>
+          caches.match(e.request).then(r => r || caches.match('/login.html'))
+        )
+    );
+    return;
+  }
+
+  // Static assets: cache-first, populate on miss
+  e.respondWith(
+    caches.match(e.request).then(cached => {
+      if (cached) return cached;
+      return fetch(e.request).then(r => {
+        if (r.ok) {
+          const clone = r.clone();
+          caches.open(CACHE).then(c => c.put(e.request, clone));
+        }
+        return r;
+      });
+    })
+  );
+});