feat: initial commit — backend API + student cabinet frontend

- Go backend: auth (JWT), points earn/spend, QR token generation,
  partners, admin grant/stats endpoints with chi router
- Next.js 14 frontend: login, student dashboard, transaction history,
  QR display, partners list
- PostgreSQL migrations (4 tables), Redis cache, Docker Compose
- CORS middleware, role-based route protection, Zustand auth store

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

frontend/components/ui/Button.tsx

@@ -0,0 +1,36 @@
+import { type ButtonHTMLAttributes } from 'react';
+
+type Variant = 'primary' | 'secondary' | 'ghost';
+
+interface ButtonProps extends ButtonHTMLAttributes<HTMLButtonElement> {
+  variant?: Variant;
+  isLoading?: boolean;
+}
+
+const VARIANT_CLASSES: Record<Variant, string> = {
+  primary: 'bg-blue-600 text-white hover:bg-blue-500 disabled:bg-blue-800 disabled:text-blue-400',
+  secondary: 'bg-gray-700 text-gray-200 hover:bg-gray-600 disabled:opacity-50',
+  ghost: 'bg-transparent text-blue-400 hover:bg-gray-700 disabled:opacity-50',
+};
+
+export function Button({
+  variant = 'primary',
+  isLoading = false,
+  disabled,
+  children,
+  className = '',
+  ...props
+}: ButtonProps) {
+  return (
+    <button
+      disabled={disabled ?? isLoading}
+      className={`inline-flex items-center justify-center gap-2 rounded-lg px-4 py-2 text-sm font-medium transition-colors focus:outline-none focus:ring-2 focus:ring-blue-500 focus:ring-offset-2 focus:ring-offset-gray-900 ${VARIANT_CLASSES[variant]} ${className}`}
+      {...props}
+    >
+      {isLoading && (
+        <span className="h-4 w-4 animate-spin rounded-full border-2 border-current border-t-transparent" />
+      )}
+      {children}
+    </button>
+  );
+}