PWA offline error page + login page cleanup (#327)

* Add friendly PWA offline error page

When the PWA fails to connect to the server, users now see a branded
offline page with a friendly "technical difficulties" message, the
app logo, and a reload button. The page automatically attempts to
reload when connectivity is restored.

Changes:
- Created public/offline.html with branded offline experience
- Updated service worker to cache and serve offline page on network failures
- Added service worker registration in application.js
- Service worker now handles navigation requests with offline fallback

* Extract PWA offline logo to separate cached asset

Move the inline SVG logo from offline.html to a separate file at
public/logo-offline.svg. This makes the logo asset easily identifiable
and maintainable, as it may diverge from other logo versions in the future.

Changes:
- Created public/logo-offline.svg with the offline page logo
- Updated service worker to cache logo as part of OFFLINE_ASSETS array
- Updated fetch handler to serve cached offline assets
- Updated offline.html to reference logo file instead of inline SVG

* Update offline message for better readability

Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>

* CodeRabbit comments

* Keep 40x and 50x flowing

* Dark mode

* Logo tweaks

* Login/sign up cleanup

---------

Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>

app/views/layouts/auth.html.erb

@@ -4,12 +4,9 @@
       <div class="grow flex flex-col justify-center">
         <div class="sm:mx-auto sm:w-full sm:max-w-md">
           <div class="flex justify-center mt-2 md:mb-6">
-            <%= image_tag "logo-color.png", class: "w-16 mb-6" %>
+            <%= image_tag "logomark.svg", class: "w-16 mb-6" %>
           </div>
           <div class="space-y-2">
-            <h2 class="text-3xl font-medium text-primary text-center">
-              <%= content_for?(:header_title) ? yield(:header_title).html_safe : t(".your_account") %>
-            </h2>
             <% if (controller_name == "sessions" && action_name == "new") || (controller_name == "registrations" && action_name == "new") %>
               <div class="space-y-3 md:hidden w-full my-4">
                 <div class="bg-surface-inset rounded-lg p-1 flex">

app/views/pwa/service-worker.js

@@ -1,10 +1,69 @@
+const CACHE_VERSION = 'v1';
+const OFFLINE_ASSETS = [
+  '/offline.html',
+  '/logo-offline.svg'
+];
+
+// Install event - cache the offline page and assets
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_VERSION).then((cache) => {
+      return cache.addAll(OFFLINE_ASSETS);
+    })
+  );
+  // Activate immediately
+  self.skipWaiting();
+});
+
+// Activate event - clean up old caches
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then((cacheNames) => {
+      return Promise.all(
+        cacheNames.map((cacheName) => {
+          if (cacheName !== CACHE_VERSION) {
+            return caches.delete(cacheName);
+          }
+        })
+      );
+    }).then(() => {
+      // Take control of all pages immediately
+      return self.clients.claim();
+    })
+  );
+});
+
+// Fetch event - serve offline page when network fails
+self.addEventListener('fetch', (event) => {
+  // Handle navigation requests (page loads)
+  if (event.request.mode === 'navigate') {
+    event.respondWith(
+      fetch(event.request).catch((error) => {
+        // Only show offline page for network errors
+        if (error.name === 'TypeError' || !navigator.onLine) {
+          return caches.match('/offline.html');
+        }
+        throw error;
+      })
+    );
+  }
+  // Handle offline assets (logo, etc.)
+  else if (OFFLINE_ASSETS.some(asset => new URL(event.request.url).pathname === asset)) {
+    event.respondWith(
+      caches.match(event.request).then((response) => {
+        return response || fetch(event.request);
+      })
+    );
+  }
+});
+
 // Add a service worker for processing Web Push notifications:
 //
 // self.addEventListener("push", async (event) => {
 //   const { title, options } = await event.data.json()
 //   event.waitUntil(self.registration.showNotification(title, options))
 // })
-// 
+//
 // self.addEventListener("notificationclick", function(event) {
 //   event.notification.close()
 //   event.waitUntil(
@@ -12,12 +71,12 @@
 //       for (let i = 0; i < clientList.length; i++) {
 //         let client = clientList[i]
 //         let clientPath = (new URL(client.url)).pathname
-// 
+//
 //         if (clientPath == event.notification.data.path && "focus" in client) {
 //           return client.focus()
 //         }
 //       }
-// 
+//
 //       if (clients.openWindow) {
 //         return clients.openWindow(event.notification.data.path)
 //       }

app/views/sessions/new.html.erb

@@ -1,7 +1,3 @@
-<%
-  header_title t(".title")
-%>
-
 <% if @prefill_demo_credentials %>
   <div class="mb-4 rounded-lg border bg-blue-50 text-blue-700 border-blue-200 theme-dark:bg-blue-900/20 theme-dark:text-blue-400 theme-dark:border-blue-800 p-4" role="status" aria-live="polite">
     <div class="flex items-start gap-3">