fix(11): wire handleDragEnd to Reorder.Group for active threads

onPointerUp was incorrectly placed on the resolved-thread div instead
of the active-thread Reorder.Group, causing drag reorder to not persist.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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

@@ -195,6 +195,7 @@ function ThreadDetailPage() {
 						axis="y"
 						values={displayItems}
 						onReorder={setTempItems}
+						onPointerUp={handleDragEnd}
 						className="flex flex-col gap-2"
 					>
 						{displayItems.map((candidate, index) => (
@@ -213,7 +214,7 @@ function ThreadDetailPage() {
 						))}
 					</Reorder.Group>
 				) : (
-					<div className="flex flex-col gap-2" onPointerUp={handleDragEnd}>
+					<div className="flex flex-col gap-2">
 						{displayItems.map((candidate, index) => (
 							<CandidateListItem
 								key={candidate.id}