feat(04-01): update thread service, routes, and hooks for categoryId

- createThread now inserts categoryId from data
- getAllThreads joins categories table, returns categoryName/categoryEmoji
- updateThread accepts optional categoryId
- ThreadListItem interface includes category fields
- useCreateThread hook sends categoryId
- Fix test files to pass categoryId when creating threads

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

src/client/hooks/useThreads.ts

@@ -6,6 +6,9 @@ interface ThreadListItem {
   name: string;
   status: "active" | "resolved";
   resolvedCandidateId: number | null;
+  categoryId: number;
+  categoryName: string;
+  categoryEmoji: string;
   createdAt: string;
   updatedAt: string;
   candidateCount: number;
@@ -60,7 +63,7 @@ export function useThread(threadId: number | null) {
 export function useCreateThread() {
   const queryClient = useQueryClient();
   return useMutation({
-    mutationFn: (data: { name: string }) =>
+    mutationFn: (data: { name: string; categoryId: number }) =>
       apiPost<ThreadListItem>("/api/threads", data),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ["threads"] });