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/dashboard/DashboardSidebar.tsx

@@ -73,15 +73,22 @@ export function DashboardSidebar() {
               <div className="flex min-w-0 flex-1 flex-col gap-0.5">
                 <span className="truncate text-sm font-medium leading-none text-foreground">{user.name}</span>
                 <span className="truncate text-xs leading-none text-muted-foreground">{user.email}</span>
-                <Badge
-                  variant="secondary"
-                  className={cn(
-                    'mt-0.5 w-fit text-xs',
-                    user.tier !== 'free' && user.tier && 'border border-primary/20 bg-primary/10 text-primary'
+                <div className="flex items-center gap-1.5">
+                  <Badge
+                    variant="secondary"
+                    className={cn(
+                      'text-xs',
+                      user.tier !== 'free' && user.tier && 'border border-primary/20 bg-primary/10 text-primary'
+                    )}
+                  >
+                    {translateTier(t, user.tier)}
+                  </Badge>
+                  {(!user.tier || user.tier === 'free') && (
+                    <Link href="/pricing" className="text-xs font-medium text-primary hover:underline">
+                      {t('dashboard.sidebar.upgradeToPro', { defaultValue: 'Passer Pro →' })}
+                    </Link>
                   )}
-                >
-                  {translateTier(t, user.tier)}
-                </Badge>
+                </div>
               </div>
               <ThemeToggle />
             </div>

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>