CopyButton never resets its checkmark after copying #1761

Description

CopyButton swaps to a check icon after a click, but the check never reverts to the clipboard icon reliably. The 2s reset timer is started in a useEffect with an empty dependency array, so it runs once on mount, not when the user copies.

Where:
packages/ui/copy-button.tsx:26-30

useEffect(() => {
	setTimeout(() => {
		setHasCopied(false)
	}, 2000)
}, [])

Steps to reproduce:

1. Render <CopyButton value="x" />.
2. Wait more than 2 seconds.
3. Click the button.

Expected behavior:
The check icon shows for about 2 seconds, then returns to the clipboard icon.

Actual behavior:
The check icon stays forever, because the only timer already fired on mount. Clicking before the mount timer fires has the opposite problem: the icon resets early, at 2s after mount rather than 2s after the click. The timer is also never cleared on unmount.

Suggested fix:
Run the effect on [hasCopied], only start the timeout when hasCopied is true, and return a clearTimeout cleanup. This is the same pattern CopyableCell already uses in packages/ui/copyable-cell.tsx:22-29:

useEffect(() => {
	if (!hasCopied) return
	const timeout = setTimeout(() => setHasCopied(false), 2000)
	return () => clearTimeout(timeout)
}, [hasCopied])

Happy to send a PR for this if it's welcome.