refactor(footer, header, robots): enhance accessibility, improve formatting, and update sitemap directives

app/components/Header.tsx

@@ -42,6 +42,7 @@ export default function Header() {
                         <button
                             className="text-gray-700 hover:text-gray-900 md:hidden"
                             onClick={toggleSidebar}
+                            aria-label={isSidebarOpen ? "Close menu" : "Open menu"}
                         >
                             <svg
                                 className="w-6 h-6"
@@ -123,7 +124,7 @@ export default function Header() {
                         Contact
                     </button>
                 </div>
-                <h6 className="text-center text-xs text-gray-500 p-4">© 2025 Dennis</h6>
+                <p className="text-center text-xs text-gray-500 p-4">© 2025 Dennis</p>
             </div>
         </div>
     );