Restructure project to root layout

public/service-worker.js

@@ -0,0 +1,48 @@
+const CACHE_NAME = 'stockfill-cache-v1';
+const OFFLINE_URLS = ['/', '/index.html'];
+
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then((cache) => {
+      return cache.addAll(OFFLINE_URLS);
+    }),
+  );
+});
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then((keys) =>
+      Promise.all(
+        keys.map((key) => {
+          if (key !== CACHE_NAME) {
+            return caches.delete(key);
+          }
+          return undefined;
+        }),
+      ),
+    ),
+  );
+});
+
+self.addEventListener('fetch', (event) => {
+  const { request } = event;
+  if (request.method !== 'GET') return;
+
+  event.respondWith(
+    fetch(request)
+      .then((response) => {
+        const copy = response.clone();
+        caches.open(CACHE_NAME).then((cache) => cache.put(request, copy));
+        return response;
+      })
+      .catch(async () => {
+        const cached = await caches.match(request);
+        if (cached) return cached;
+        if (request.mode === 'navigate') {
+          const fallback = await caches.match('/index.html');
+          if (fallback) return fallback;
+        }
+        throw new Error('Network error');
+      }),
+  );
+});