chore: restructure project into backend and frontend folders

- Move all frontend code to frontend/ directory
- Add backend/ with Go project structure (cmd, internal, pkg)
- Add docker-compose.yml for orchestration

frontend/src/components/ui/Input.tsx

@@ -0,0 +1,25 @@
+import type { InputHTMLAttributes } from 'react';
+
+interface InputProps extends InputHTMLAttributes<HTMLInputElement> {
+  label?: string;
+  error?: string;
+}
+
+export const Input = ({ label, error, className = '', ...props }: InputProps) => {
+  return (
+    <div className="w-full">
+      {label && (
+        <label className="block text-sm font-medium text-[#1b1b1d] mb-1">
+          {label}
+        </label>
+      )}
+      <input
+        className={`w-full px-3 py-2 bg-[#f5f3f5] border border-[#c5c6cd] rounded-md text-[#1b1b1d] placeholder-[#75777d] focus:outline-none focus:ring-2 focus:ring-[#1B263B] focus:border-transparent transition-colors ${className}`}
+        {...props}
+      />
+      {error && (
+        <p className="mt-1 text-sm text-red-600">{error}</p>
+      )}
+    </div>
+  );
+};