Add secure admin panel for content moderation and contribution flagging

Adds an admin interface with authentication for manual content deletion and flagging. Implements a flagging system for user contributions and secures the admin panel with a secret token.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 923ae0e3-a363-4db8-b04a-e8baca2a1330
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Replit-Commit-Event-Id: 7e5834b1-796d-4a9e-bbde-cd91012292de
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Replit-Helium-Checkpoint-Created: true

artifacts/voix-du-peuple/src/App.tsx

@@ -7,6 +7,7 @@ import Home from "@/pages/home";
 import About from "@/pages/about";
 import Transparence from "@/pages/transparence";
 import Flyer from "@/pages/flyer";
+import Admin from "@/pages/admin";
 import { AccessibilityProvider } from "@/hooks/use-accessibility";
 import { AccessibilityPanel } from "@/components/accessibility-panel";
 
@@ -67,6 +68,7 @@ function Router() {
           <Route path="/about" component={About} />
           <Route path="/transparence" component={Transparence} />
           <Route path="/flyer" component={Flyer} />
+          <Route path="/admin" component={Admin} />
           <Route component={NotFound} />
         </Switch>
       </main>