feat(chat): reveal user message edit/copy actions on tap (mobile)

The Edit and Copy buttons on user messages were only shown via CSS
:hover (group-hover:flex / hover:flex), so they were unreachable on
touch devices. Wire the existing per-message isTapped toggle to reveal
them on tap, scoped to (hover: none) devices so desktop hover behavior
is unchanged.

Author: gary149

src/lib/components/chat/ChatMessage.svelte

@@ -631,7 +631,9 @@
 				{/if}
 				{#if (alternatives.length > 1 && editMsdgId === null) || (!loading && !editMode)}
 					<button
-						class="hidden h-5 cursor-pointer items-center gap-1 rounded-md px-1.5 py-0.5 text-xs text-gray-400 group-hover:flex hover:flex hover:bg-gray-100 hover:text-gray-500 lg:-right-2 dark:text-gray-400 dark:hover:bg-gray-800 dark:hover:text-gray-300"
+						class="hidden h-5 cursor-pointer items-center gap-1 rounded-md px-1.5 py-0.5 text-xs text-gray-400 group-hover:flex hover:flex hover:bg-gray-100 hover:text-gray-500 lg:-right-2 dark:text-gray-400 dark:hover:bg-gray-800 dark:hover:text-gray-300 {isTapped
+							? '[@media(hover:none)]:flex'
+							: ''}"
 						title="Edit"
 						type="button"
 						onclick={() => {
@@ -643,7 +645,9 @@
 						Edit
 					</button>
 					<button
-						class="hidden h-5 cursor-pointer items-center gap-1 rounded-md px-1.5 py-0.5 text-xs group-hover:flex hover:flex hover:bg-gray-100 lg:-right-2 dark:hover:bg-gray-800 {isUserMsgCopied
+						class="hidden h-5 cursor-pointer items-center gap-1 rounded-md px-1.5 py-0.5 text-xs group-hover:flex hover:flex hover:bg-gray-100 lg:-right-2 dark:hover:bg-gray-800 {isTapped
+							? '[@media(hover:none)]:flex'
+							: ''} {isUserMsgCopied
 							? 'text-green-500 dark:text-green-400'
 							: 'text-gray-400 hover:text-gray-500 dark:text-gray-400 dark:hover:text-gray-300'}"
 						title="Copy to clipboard"