remove theme toggle adn add link to chessboard route

src/components/Header.tsx

@@ -1,5 +1,4 @@
 import { Link } from '@tanstack/react-router'
-import ThemeToggle from './ThemeToggle'
 
 export default function Header() {
   return (
@@ -24,20 +23,12 @@ export default function Header() {
             Home
           </Link>
           <Link
-            to="/about"
+            to="/chessboard"
             className="nav-link"
             activeProps={{ className: 'nav-link is-active' }}
           >
-            About
+            Chessboard
           </Link>
-          <a
-            href="https://tanstack.com/start/latest/docs/framework/react/overview"
-            className="nav-link"
-            target="_blank"
-            rel="noreferrer"
-          >
-            Docs
-          </a>
         </div>
 
         <div className="ml-auto flex items-center gap-1.5 sm:gap-2">
@@ -70,7 +61,6 @@ export default function Header() {
             </svg>
           </a>
 
-          <ThemeToggle />
         </div>
       </nav>
     </header>