fix: skip retries on 404 for single-resource queries

Prevents 10-second loading skeleton when navigating to non-existent
threads, setups, or items. Shows error/not-found state immediately.

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

src/client/hooks/useThreads.ts

@@ -1,5 +1,5 @@
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
-import { apiDelete, apiGet, apiPost, apiPut } from "../lib/api";
+import { ApiError, apiDelete, apiGet, apiPost, apiPut } from "../lib/api";
 
 interface ThreadListItem {
 	id: number;
@@ -61,6 +61,8 @@ export function useThread(threadId: number | null) {
 		queryKey: ["threads", threadId],
 		queryFn: () => apiGet<ThreadWithCandidates>(`/api/threads/${threadId}`),
 		enabled: threadId != null,
+		retry: (count, error) =>
+			error instanceof ApiError && error.status === 404 ? false : count < 3,
 	});
 }