chore: import upstream snapshot with attribution

apps/docs/components/ui/heading.tsx

@@ -0,0 +1,58 @@
+'use client'
+
+import { type ComponentPropsWithoutRef, useState } from 'react'
+import { Check, Link } from 'lucide-react'
+import { cn } from '@/lib/utils'
+
+type HeadingTag = 'h1' | 'h2' | 'h3' | 'h4' | 'h5' | 'h6'
+
+interface HeadingProps extends ComponentPropsWithoutRef<'h1'> {
+  as?: HeadingTag
+}
+
+export function Heading({ as, className, ...props }: HeadingProps) {
+  const [copied, setCopied] = useState(false)
+  const As = as ?? 'h1'
+
+  if (!props.id) {
+    return <As className={className} {...props} />
+  }
+
+  const copyHeadingLink = async (e: React.MouseEvent) => {
+    e.preventDefault()
+
+    const url = `${window.location.origin}${window.location.pathname}#${props.id}`
+
+    try {
+      await navigator.clipboard.writeText(url)
+      setCopied(true)
+
+      // Update URL hash without scrolling
+      window.history.pushState(null, '', `#${props.id}`)
+
+      setTimeout(() => setCopied(false), 2000)
+    } catch {
+      // Fallback: just navigate to the anchor
+      window.location.hash = props.id as string
+    }
+  }
+
+  return (
+    <As className={cn('group flex scroll-m-28 flex-row items-center gap-2', className)} {...props}>
+      <a href={`#${props.id}`} className='peer' onClick={copyHeadingLink}>
+        {props.children}
+      </a>
+      {copied ? (
+        <Check
+          aria-hidden
+          className='size-[14px] shrink-0 text-[var(--brand-accent)] opacity-100 transition-opacity'
+        />
+      ) : (
+        <Link
+          aria-hidden
+          className='size-[14px] shrink-0 text-[var(--text-icon)] opacity-0 transition-opacity group-hover:opacity-100 peer-hover:opacity-100'
+        />
+      )}
+    </As>
+  )
+}