🔧 chore(repo): restructure project file hierarchy

- move project files out of fleetledger directory to root
- update .gitignore to reflect new .env path

📝 docs(README): add detailed project description

- provide an overview of FleetLedger's features and usage
- include setup instructions and security notes

app/static/service-worker.js

@@ -0,0 +1,74 @@
+const CACHE_VERSION = "v2";
+const CACHE_NAME = `fleetledger-${CACHE_VERSION}`;
+const ASSETS = [
+  "/",
+  "/static/style.css",
+  "/static/icon-192.png",
+  "/static/icon-512.png",
+  "/static/manifest.webmanifest",
+];
+
+self.addEventListener("install", (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then((cache) => {
+      return cache.addAll(ASSETS);
+    })
+  );
+});
+
+self.addEventListener("activate", (event) => {
+  event.waitUntil(
+    caches.keys().then((keys) =>
+      Promise.all(
+        keys
+          .filter((key) => key.startsWith("fleetledger-") && key !== CACHE_NAME)
+          .map((key) => caches.delete(key))
+      )
+    )
+  );
+});
+
+async function networkFirst(request) {
+  try {
+    const response = await fetch(request);
+    const cache = await caches.open(CACHE_NAME);
+    cache.put(request, response.clone());
+    return response;
+  } catch (err) {
+    const cached = await caches.match(request);
+    if (cached) {
+      return cached;
+    }
+    return caches.match("/");
+  }
+}
+
+async function cacheFirst(request) {
+  const cached = await caches.match(request);
+  if (cached) {
+    return cached;
+  }
+  const response = await fetch(request);
+  const cache = await caches.open(CACHE_NAME);
+  cache.put(request, response.clone());
+  return response;
+}
+
+self.addEventListener("fetch", (event) => {
+  if (event.request.method !== "GET") {
+    return;
+  }
+
+  const url = new URL(event.request.url);
+
+  // Navigation requests: network first, fallback to cache
+  if (event.request.mode === "navigate") {
+    event.respondWith(networkFirst(event.request));
+    return;
+  }
+
+  // Same-origin static assets: cache first
+  if (url.origin === self.location.origin) {
+    event.respondWith(cacheFirst(event.request));
+  }
+});