Fix Join Us button linking logged-in users to register page

Send logged-in users to their dashboard instead of the registration
form, matching how the Navbar already treats logged-in vs guest users.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/app/page.tsx

@@ -1,8 +1,9 @@
 import { EventCard } from "@/components/events/EventCard";
 import { Navbar } from "@/components/layout/Navbar";
 import { Footer } from "@/components/layout/Footer";
+import { JoinUsButton } from "@/components/home/JoinUsButton";
 import { appName } from "@/lib/siteConfig";
-import { Calendar, UserPlus, ArrowRight, CalendarCheck, Users, Heart, ShieldCheck } from "lucide-react";
+import { Calendar, ArrowRight, CalendarCheck, Users, Heart, ShieldCheck } from "lucide-react";
 
 type Event = {
   id: string;
@@ -58,10 +59,7 @@ export default async function HomePage() {
                                 <Calendar className="w-4 h-4" />
                                 View Events
                             </a>
-                            <a href="/register" className="inline-flex items-center gap-2 px-6 py-2.5 border border-brand-600 text-brand-600 rounded-xl hover:bg-brand-50 font-medium transition-colors">
-                                <UserPlus className="w-4 h-4" />
-                                Join Us
-                            </a>
+                            <JoinUsButton />
                         </div>
                     </div>
                 </section>