feat: add PWA support with offline caching

- Generate 192x192, 512x512 and Apple touch icons from favicon.svg
- Add web app manifest (manifest.json)
- Add service worker with network-first for HTML, cache-first for assets
- Register SW in BaseLayout
- Add theme-color meta and apple-touch-icon link

public/sw.js

@@ -0,0 +1,52 @@
+const CACHE_NAME = 'randify-v1';
+
+self.addEventListener('install', (event) => {
+  self.skipWaiting();
+});
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(self.clients.claim());
+});
+
+self.addEventListener('fetch', (event) => {
+  const { request } = event;
+  const isNavigate = request.mode === 'navigate';
+  const isSameOrigin = new URL(request.url).origin === self.location.origin;
+
+  if (!isSameOrigin) {
+    return;
+  }
+
+  if (isNavigate) {
+    // Network-first for HTML pages: fresh content when online,
+    // fallback to cache when offline.
+    event.respondWith(
+      fetch(request)
+        .then((response) => {
+          if (response && response.status === 200) {
+            const clone = response.clone();
+            caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
+          }
+          return response;
+        })
+        .catch(() => caches.match(request))
+    );
+  } else {
+    // Cache-first for static assets (JS, CSS, SVG, fonts, etc.)
+    event.respondWith(
+      caches.match(request).then((cached) => {
+        if (cached) {
+          return cached;
+        }
+        return fetch(request).then((response) => {
+          if (!response || response.status !== 200 || response.type !== 'basic') {
+            return response;
+          }
+          const clone = response.clone();
+          caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
+          return response;
+        });
+      })
+    );
+  }
+});