feat: add GDPR cookie consent banner and upgrade-to-Pro link

- Cookie consent banner with accept all / essential only buttons
- Uses existing i18n messages (en/fr) and localStorage for persistence
- Animated with Framer Motion, respects dark/light theme
- Free tier users see "Passer Pro →" link next to their badge in sidebar

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/app/layout.tsx

@@ -7,6 +7,7 @@ import { NotificationProvider } from "@/components/ui/notification";
 import { I18nProvider } from "@/lib/i18n";
 import { Agentation } from "agentation";
 import { GoogleOAuthProvider } from "@react-oauth/google";
+import { CookieConsent } from "@/components/ui/cookie-consent";
 
 export const dynamic = 'force-dynamic';
 
@@ -33,6 +34,7 @@ export default function RootLayout({
               <GoogleOAuthProvider clientId={process.env.NEXT_PUBLIC_GOOGLE_CLIENT_ID || ""}>
                 <NotificationProvider>
                   {children}
+                  <CookieConsent />
                 </NotificationProvider>
               </GoogleOAuthProvider>
             </QueryProvider>