Add dark mode toggle

src/components/layout/Header.tsx

@@ -7,6 +7,7 @@ import { Badge } from '@/components/ui/badge';
 import { Link, useNavigate } from 'react-router-dom';
 import { SearchDropdown } from '@/components/search/SearchDropdown';
 import { AuthButtons } from '@/components/auth/AuthButtons';
+import { ThemeToggle } from '@/components/theme/ThemeToggle';
 
 export function Header() {
   const navigate = useNavigate();
@@ -67,6 +68,7 @@ export function Header() {
 
         {/* User Actions */}
         <div className="flex items-center gap-2">
+          <ThemeToggle />
           <AuthButtons />
           
           {/* Mobile Menu */}
@@ -105,6 +107,9 @@ export function Header() {
                   🏭 Manufacturers
                 </Button>
                 <div className="border-t pt-4 mt-4">
+                  <div className="mb-3">
+                    <ThemeToggle />
+                  </div>
                   <Button variant="outline" className="w-full mb-2">
                     Sign In
                   </Button>