Add admin dashboard and Replit authentication integration

Integrates Replit authentication using OpenID Connect, adds an admin dashboard route with video management and thumbnail upload capabilities, and updates dependencies.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 890577b1-c154-40a4-a177-a0c6d55320c3
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/8cc42625-c1f5-4e43-99bd-77f2c4dedee2/890577b1-c154-40a4-a177-a0c6d55320c3/1jMBtLj

client/src/App.tsx

@@ -8,6 +8,7 @@ import VideoPage from "@/pages/VideoPage";
 import FolxStadlPage from "@/pages/FolxStadlPage";
 import GeschichteLiedPage from "@/pages/GeschichteLiedPage";
 import GipfelstammtischPage from "@/pages/GipfelstammtischPage";
+import AdminPage from "@/pages/admin";
 import NotFound from "@/pages/not-found";
 
 function Router() {
@@ -18,6 +19,7 @@ function Router() {
       <Route path="/folx-stadl" component={FolxStadlPage} />
       <Route path="/geschichte-lied" component={GeschichteLiedPage} />
       <Route path="/gipfelstammtisch" component={GipfelstammtischPage} />
+      <Route path="/admin" component={AdminPage} />
       <Route component={NotFound} />
     </Switch>
   );