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/slider.tsx

@@ -0,0 +1,23 @@
+import * as React from "react";
+import * as SliderPrimitive from "@radix-ui/react-slider";
+
+import { cn } from "@/lib/utils";
+
+const Slider = React.forwardRef<
+  React.ElementRef<typeof SliderPrimitive.Root>,
+  React.ComponentPropsWithoutRef<typeof SliderPrimitive.Root>
+>(({ className, ...props }, ref) => (
+  <SliderPrimitive.Root
+    ref={ref}
+    className={cn("relative flex w-full touch-none select-none items-center", className)}
+    {...props}
+  >
+    <SliderPrimitive.Track className="relative h-2 w-full grow overflow-hidden rounded-full bg-secondary">
+      <SliderPrimitive.Range className="absolute h-full bg-primary" />
+    </SliderPrimitive.Track>
+    <SliderPrimitive.Thumb className="block h-5 w-5 rounded-full border-2 border-primary bg-background ring-offset-background transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 disabled:pointer-events-none disabled:opacity-50" />
+  </SliderPrimitive.Root>
+));
+Slider.displayName = SliderPrimitive.Root.displayName;
+
+export { Slider };