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/confidentialite/page.tsx

@@ -12,7 +12,7 @@ export const metadata: Metadata = {
 
 export default function Confidentialite() {
   return (
-    <main className="min-h-screen py-20 md:py-32">
+    <main className="min-h-screen py-20 md:py-32 bg-dark">
       <div className="max-w-3xl mx-auto px-4 sm:px-6">
         <Link href="/" className="inline-flex items-center gap-2 mb-10 text-white/40 hover:text-white text-sm transition-colors">
           <svg className="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">