feat(web): add base UI components

- Button with variants (default, destructive, outline, secondary, ghost, link, success)
- Input with consistent styling
- Card with Header, Title, Description, Content, Footer
- Label using Radix UI primitives
- Index file for centralized exports

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/components/ui/input.tsx

@@ -0,0 +1,24 @@
+import * as React from 'react';
+import { cn } from '@/lib/utils';
+
+export interface InputProps
+  extends React.InputHTMLAttributes<HTMLInputElement> {}
+
+const Input = React.forwardRef<HTMLInputElement, InputProps>(
+  ({ className, type, ...props }, ref) => {
+    return (
+      <input
+        type={type}
+        className={cn(
+          'flex h-10 w-full rounded-md border border-input bg-background px-3 py-2 text-sm ring-offset-background file:border-0 file:bg-transparent file:text-sm file:font-medium 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}
+      />
+    );
+  }
+);
+Input.displayName = 'Input';
+
+export { Input };