fix: prevent snap-back after drag and click-opens-edit during drag

Two fixes:
- Remove onSettled clearing tempItems before refetch completes,
  let useEffect clear it when fresh server data arrives
- Track isDragging ref to suppress edit panel click after drag
- Remove layout="position" which interfered with reorder detection

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/routes/threads/$threadId.tsx

@@ -87,10 +87,9 @@ function ThreadDetailPage() {
 
 	function handleDragEnd() {
 		if (!tempItems) return;
-		reorderMutation.mutate(
-			{ orderedIds: tempItems.map((c) => c.id) },
-			{ onSettled: () => setTempItems(null) },
-		);
+		reorderMutation.mutate({
+			orderedIds: tempItems.map((c) => c.id),
+		});
 	}
 
 	return (