fix: use onDragEnd on Reorder.Item instead of onPointerUp on Group

The previous approach used onPointerUp on the Reorder.Group which
fired unreliably — triggering on non-drag clicks and sometimes not
at all after a drag. Moving to onDragEnd on each Reorder.Item gives
clean, predictable drag-to-reorder behavior.

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

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

@@ -36,12 +36,11 @@ function ThreadDetailPage() {
 		thread?.categoryId ?? 0,
 	);
 
-	const [tempItems, setTempItems] =
-		useState<typeof thread extends { candidates: infer C } ? C : never | null>(
-			null,
-		);
+	const [tempItems, setTempItems] = useState<
+		NonNullable<typeof thread>["candidates"] | null
+	>(null);
 
-	// Clear tempItems when server data changes (biome-ignore: thread?.candidates is intentional dep)
+	// Clear tempItems when server data changes
 	// biome-ignore lint/correctness/useExhaustiveDependencies: thread?.candidates is the intended trigger
 	useEffect(() => {
 		setTempItems(null);
@@ -227,7 +226,6 @@ function ThreadDetailPage() {
 						axis="y"
 						values={displayItems}
 						onReorder={setTempItems}
-						onPointerUp={handleDragEnd}
 						className="flex flex-col gap-2"
 					>
 						{displayItems.map((candidate, index) => (
@@ -243,6 +241,7 @@ function ThreadDetailPage() {
 									})
 								}
 								delta={deltas[candidate.id]}
+								onDragEnd={handleDragEnd}
 							/>
 						))}
 					</Reorder.Group>