fix: add dark backgrounds to all internal pages + RGPD cookie banner

- login, register, candidature, cgv, confidentialite, mentions-legales:
  add bg-dark class so white text is visible on dark background
- admin shell + protected layout: same fix for admin/dashboard pages
- CookieBanner: update styling to match navy/orange branding, add RGPD
  compliance text, include Accepter/Refuser buttons, link to confidentialite
- layout.tsx: import and render CookieBanner globally

https://claude.ai/code/session_01V8YAjpqRQ3bfBYsABYsEgo

app/layout.tsx

@@ -1,4 +1,5 @@
 import type { Metadata } from "next";
+import CookieBanner from "@/components/CookieBanner";
 import "./globals.css";
 
 const BASE_URL = process.env.NEXT_PUBLIC_APP_URL || "https://hooklab.eu";
@@ -224,6 +225,7 @@ export default function RootLayout({
           Aller au contenu principal
         </a>
         {children}
+        <CookieBanner />
       </body>
     </html>
   );