Add authentication system with landing page

src/pages/login.astro

@@ -0,0 +1,21 @@
+---
+import '@/styles/globals.css'
+import Layout from '../layouts/Layout.astro';
+import { AuthForm } from '../components/AuthForm';
+import { Navbar } from '../components/Navbar';
+---
+
+<Layout title="Sign In - InboxNegotiator">
+  <Navbar client:load />
+  
+  <main class="min-h-screen bg-gray-50 flex items-center justify-center py-12 px-4 sm:px-6 lg:px-8">
+    <div class="w-full max-w-md">
+      <div class="text-center mb-8">
+        <h1 class="text-3xl font-bold text-gray-900 mb-2">Sign In</h1>
+        <p class="text-gray-600">Access your debt resolution dashboard</p>
+      </div>
+      
+      <AuthForm mode="login" client:load />
+    </div>
+  </main>
+</Layout>