feat: make Button polymorphic — renders <a> when href is provided

Discriminated union types (AsButton | AsAnchor), isAnchorProps type guard
eliminates all 'as' casts. as const satisfies for VARIANTS/SIZES lookup
tables. brutal-border replaces border-[3px] in ghost variant.

src/shared/ui/Button/ui/Button.test.tsx

@@ -63,4 +63,31 @@ describe('Button', () => {
       expect(screen.getByRole('button')).toHaveClass('w-full');
     });
   });
+  describe('as anchor', () => {
+    it('renders an anchor when href is provided', () => {
+      render(<Button href="/cv.pdf">Download</Button>);
+      expect(screen.getByRole('link', { name: 'Download' })).toBeInTheDocument();
+    });
+    it('sets href on the anchor', () => {
+      render(<Button href="/cv.pdf">Download</Button>);
+      expect(screen.getByRole('link')).toHaveAttribute('href', '/cv.pdf');
+    });
+    it('sets download attribute when provided', () => {
+      render(
+        <Button href="/cv.pdf" download>
+          Download
+        </Button>,
+      );
+      expect(screen.getByRole('link')).toHaveAttribute('download');
+    });
+    it('applies the same variant and size classes as button', () => {
+      render(
+        <Button href="/test" variant="primary" size="sm">
+          Go
+        </Button>,
+      );
+      const link = screen.getByRole('link');
+      expect(link).toHaveClass('bg-blue', 'px-4', 'py-2');
+    });
+  });
 });

src/shared/ui/Button/ui/Button.tsx

@@ -1,10 +1,10 @@
-import type { ButtonHTMLAttributes, ReactNode } from 'react';
+import type { AnchorHTMLAttributes, ButtonHTMLAttributes, ReactNode } from 'react';
 import { cn } from '$shared/lib';
 
 export type ButtonVariant = 'primary' | 'secondary' | 'outline' | 'ghost';
 export type ButtonSize = 'sm' | 'md' | 'lg';
 
-interface Props extends ButtonHTMLAttributes<HTMLButtonElement> {
+type BaseProps = {
   /**
    * Visual variant
    * @default 'primary'
@@ -19,9 +19,28 @@ interface Props extends ButtonHTMLAttributes<HTMLButtonElement> {
    * Button content
    */
   children: ReactNode;
+  /**
+   * CSS classes
+   */
+  className?: string;
+};
+
+type AsButton = BaseProps & ButtonHTMLAttributes<HTMLButtonElement> & { href?: never };
+type AsAnchor = BaseProps & AnchorHTMLAttributes<HTMLAnchorElement> & { href: string };
+
+type Props = AsButton | AsAnchor;
+
+type RestButton = Omit<AsButton, keyof BaseProps>;
+type RestAnchor = Omit<AsAnchor, keyof BaseProps>;
+
+/**
+ * Narrows spread props to anchor shape when href is a non-undefined string.
+ */
+function isAnchorProps(props: RestButton | RestAnchor): props is RestAnchor {
+  return typeof props.href === 'string';
 }
 
-const VARIANTS: Record<ButtonVariant, string> = {
+const VARIANTS = {
   primary:
     'brutal-border bg-blue text-cream shadow-[5px_5px_0_rgba(4,28,243,0.35)] hover:-translate-x-0.5 hover:-translate-y-0.5 hover:shadow-[7px_7px_0_rgba(4,28,243,0.35)] active:translate-x-0.5 active:translate-y-0.5 active:shadow-[1px_1px_0_rgba(4,28,243,0.35)]',
   secondary:
@@ -29,14 +48,14 @@ const VARIANTS: Record<ButtonVariant, string> = {
   outline:
     'brutal-border bg-transparent text-blue shadow-brutal hover:-translate-x-0.5 hover:-translate-y-0.5 hover:shadow-brutal-md active:translate-x-0.5 active:translate-y-0.5 active:shadow-brutal-xs',
   ghost:
-    'border-[3px] border-solid border-blue/35 bg-cream text-blue hover:border-blue hover:bg-blue/10 active:bg-blue active:text-cream',
-};
+    'brutal-border border-blue/35 bg-cream text-blue hover:border-blue hover:bg-blue/10 active:bg-blue active:text-cream',
+} as const satisfies Record<ButtonVariant, string>;
 
-const SIZES: Record<ButtonSize, string> = {
+const SIZES = {
   sm: 'px-4 py-2 text-sm',
   md: 'px-6 py-3 text-base',
   lg: 'px-8 py-4 text-lg',
-};
+} as const satisfies Record<ButtonSize, string>;
 
 /* box-shadow excluded from transition intentionally — snaps instantly so the
  * eye follows the 130ms button movement, not the shadow change. */
@@ -44,10 +63,22 @@ const BASE = 'cursor-pointer btn-transition uppercase tracking-wider';
 
 /**
  * Brutalist button with variants and sizes.
+ * Renders as <a> when href is provided, <button> otherwise.
  */
 export function Button({ variant = 'primary', size = 'md', className, children, ...props }: Props) {
+  const cls = cn(BASE, VARIANTS[variant], SIZES[size], className);
+
+  if (isAnchorProps(props)) {
+    const { href, ...anchorProps } = props;
     return (
-    <button className={cn(BASE, VARIANTS[variant], SIZES[size], className)} {...props}>
+      <a href={href} rel="noopener noreferrer" target="_blank" className={cls} {...anchorProps}>
+        {children}
+      </a>
+    );
+  }
+
+  return (
+    <button className={cls} {...props}>
       {children}
     </button>
   );