Add landing page with shadcn/ui and dark mode

components/theme-toggle.tsx

@@ -0,0 +1,21 @@
+"use client";
+
+import { Moon, Sun } from "lucide-react";
+import { useTheme } from "next-themes";
+import { Button } from "@/components/ui/button";
+
+export function ThemeToggle() {
+  const { theme, setTheme } = useTheme();
+
+  return (
+    <Button
+      variant="ghost"
+      size="icon"
+      onClick={() => setTheme(theme === "dark" ? "light" : "dark")}
+      aria-label="Toggle theme"
+    >
+      <Sun className="size-5 rotate-0 scale-100 transition-all dark:-rotate-90 dark:scale-0" />
+      <Moon className="absolute size-5 rotate-90 scale-0 transition-all dark:rotate-0 dark:scale-100" />
+    </Button>
+  );
+}