feat: add recalculateAllElo function for idempotent ELO recalculation

src/app/admin/page.tsx

@@ -4,6 +4,7 @@ import Link from "next/link"
 import { redirect } from "next/navigation"
 import { getSession } from "@/lib/auth-simple"
 import type { Event as EventModel } from "@prisma/client"
+import { RecalculateEloButton } from "../../components/RecalculateEloButton"
 
 export default async function AdminDashboard() {
   console.log('AdminDashboard rendering...')
@@ -169,6 +170,7 @@ export default async function AdminDashboard() {
                   </svg>
                   All Tournaments
                 </Link>
+                <RecalculateEloButton />
               </div>
             </div>