refactor(portal): update root page with notice of overhaul

portal/src/routes/+layout.svelte

@@ -1,6 +1,7 @@
 <script lang="ts"></script>
 
-<div class="dark w-full h-screen min-h-screen
-            text-white bg-background">
+<div
+  class="dark w-full h-screen min-h-screen
+          text-white bg-background">
   <slot />
 </div>

portal/src/routes/+page.svelte

@@ -1,8 +1,21 @@
 <script lang="ts">
+  import * as Card from '$lib/components/ui/card';
 </script>
 
 <svelte:head>
-  <title>RIVAlumni Portal</title>
+  <title>Home - RIVAlumni Portal</title>
 </svelte:head>
 
-<p>This page is supposed to be empty for now.</p>
+<div
+  class="w-full h-full
+          flex flex-col justify-center items-center">
+  <Card.Root class="m-6 max-w-md">
+    <Card.Header>
+      <Card.Title>System is being overhauled</Card.Title>
+      <Card.Description>
+        If you are a beta-tester, please use the link provided by the System
+        Administrator.
+      </Card.Description>
+    </Card.Header>
+  </Card.Root>
+</div>