Refactor: Move theme toggle to mobile menu

src/components/layout/Header.tsx

@@ -106,6 +106,11 @@ export function Header() {
                       </Link>
                     </>
                   )}
+                  <div className="my-2 border-t border-border" />
+                  <div className="px-3 py-2.5 flex items-center justify-between">
+                    <span className="text-base font-medium">Theme</span>
+                    <ThemeToggle />
+                  </div>
                 </nav>
               </SheetContent>
             </Sheet>
@@ -235,7 +240,9 @@ export function Header() {
               <span className="sr-only">Search</span>
             </Button>
             
+            <div className="hidden md:block">
               <ThemeToggle />
+            </div>
             {user && <NotificationCenter />}
             <AuthButtons />
           </div>