feat: add frontend source code

Add search-zen-50 React SPA source code to frontend/ directory.
Build artifacts (dist, node_modules, lock files) are gitignored.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/ui/textarea.tsx

@@ -0,0 +1,21 @@
+import * as React from "react";
+
+import { cn } from "@/lib/utils";
+
+export interface TextareaProps extends React.TextareaHTMLAttributes<HTMLTextAreaElement> {}
+
+const Textarea = React.forwardRef<HTMLTextAreaElement, TextareaProps>(({ className, ...props }, ref) => {
+  return (
+    <textarea
+      className={cn(
+        "flex min-h-[80px] w-full rounded-md border border-input bg-background px-3 py-2 text-sm ring-offset-background placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 disabled:cursor-not-allowed disabled:opacity-50",
+        className,
+      )}
+      ref={ref}
+      {...props}
+    />
+  );
+});
+Textarea.displayName = "Textarea";
+
+export { Textarea };