fix(ui): mobile menu missing user section + logout, fix OG image

- AppLayout: add user info + 'My account' + 'Sign out' to mobile hamburger menu
- Header: add 'Sign out' button to authenticated mobile menu (landing page)
- dist/og-image.png: sync with public/ (Cohorta-branded, replaces Lovable image)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/layout/AppLayout.tsx

@@ -6,7 +6,7 @@ import { billingApi } from '@/lib/api';
 import Logo from '@/components/brand/Logo';
 import UserDropdown from '@/components/brand/UserDropdown';
 import LanguageSwitcher from '@/components/LanguageSwitcher';
-import { Users, MessageSquare, LayoutDashboard, CreditCard, ShieldCheck, Zap, Menu, X } from 'lucide-react';
+import { Users, MessageSquare, LayoutDashboard, CreditCard, ShieldCheck, Zap, Menu, X, LogOut, User } from 'lucide-react';
 import { cn } from '@/lib/utils';
 
 const NAV_ITEMS = [
@@ -17,7 +17,7 @@ const NAV_ITEMS = [
 ] as const;
 
 export default function AppLayout({ children }: { children?: React.ReactNode }) {
-  const { user, isAuthenticated } = useAuth();
+  const { user, isAuthenticated, logout } = useAuth();
   const navigate = useNavigate();
   const { t } = useTranslation();
   const [credits, setCredits] = useState<number | null>(null);
@@ -119,6 +119,33 @@ export default function AppLayout({ children }: { children?: React.ReactNode })
                 {t(labelKey, fallback)}
               </NavLink>
             ))}
+            {/* User section */}
+            <div className="mt-2 pt-3 border-t border-border/40 flex flex-col gap-1">
+              <div className="px-3 py-2 flex items-center gap-3">
+                <div className="h-8 w-8 rounded-full bg-primary/15 border border-primary/30 flex items-center justify-center flex-shrink-0">
+                  <span className="text-xs font-semibold text-primary">{user?.username?.slice(0, 2).toUpperCase() || 'U'}</span>
+                </div>
+                <div className="min-w-0">
+                  <p className="text-sm font-medium text-foreground truncate">{user?.username}</p>
+                  <p className="text-xs text-muted-foreground truncate">{user?.email}</p>
+                </div>
+              </div>
+              <NavLink
+                to="/dashboard"
+                className={({ isActive }) => cn('flex items-center gap-2.5 px-3 py-2.5 rounded-xl text-sm font-medium', isActive ? 'text-primary bg-primary/10' : 'text-muted-foreground hover:text-foreground hover:bg-secondary/60')}
+                onClick={() => setMobileOpen(false)}
+              >
+                <User className="h-4 w-4" />
+                My account
+              </NavLink>
+              <button
+                onClick={() => { logout(); navigate('/'); setMobileOpen(false); }}
+                className="flex items-center gap-2.5 px-3 py-2.5 rounded-xl text-sm font-medium text-destructive hover:bg-destructive/10 transition-all text-left w-full"
+              >
+                <LogOut className="h-4 w-4" />
+                Sign out
+              </button>
+            </div>
           </div>
         )}
       </header>

src/components/layout/Header.tsx

@@ -11,7 +11,7 @@ import LanguageSwitcher from '@/components/LanguageSwitcher';
 import { useTranslation } from 'react-i18next';
 
 export default function Header() {
-  const { isAuthenticated } = useAuth();
+  const { isAuthenticated, logout } = useAuth();
   const navigate = useNavigate();
   const location = useLocation();
   const { t } = useTranslation();
@@ -177,11 +177,19 @@ export default function Header() {
             </nav>
             <div className="flex flex-col gap-2 border-t border-border pt-3">
               {isAuthenticated ? (
-                <Link to="/dashboard" onClick={() => setMobileOpen(false)}>
-                  <button className="w-full px-4 py-2.5 rounded-xl text-sm font-semibold bg-primary text-primary-foreground">
-                    {t('nav.my_account')}
+                <>
+                  <Link to="/dashboard" onClick={() => setMobileOpen(false)}>
+                    <button className="w-full px-4 py-2.5 rounded-xl text-sm font-semibold bg-primary text-primary-foreground">
+                      {t('nav.my_account')}
+                    </button>
+                  </Link>
+                  <button
+                    onClick={() => { logout(); navigate('/'); setMobileOpen(false); }}
+                    className="w-full px-4 py-2.5 rounded-xl text-sm font-medium border border-border text-muted-foreground hover:text-foreground hover:bg-secondary/50 transition-all"
+                  >
+                    Sign out
                   </button>
-                </Link>
+                </>
               ) : (
                 <>
                   <Link