test(issues): add missing api mocks for agent task endpoints

Add getActiveTaskForIssue, listTasksByIssue, and listTaskMessages mocks
to the issue detail page test. These are now called unconditionally since
the assigneeType guard was removed.

apps/web/app/(dashboard)/issues/[id]/page.test.tsx

@@ -161,6 +161,9 @@ vi.mock("@/shared/api", () => ({
     listIssueSubscribers: vi.fn().mockResolvedValue([]),
     subscribeToIssue: vi.fn().mockResolvedValue(undefined),
     unsubscribeFromIssue: vi.fn().mockResolvedValue(undefined),
+    getActiveTaskForIssue: vi.fn().mockResolvedValue({ task: null }),
+    listTasksByIssue: vi.fn().mockResolvedValue([]),
+    listTaskMessages: vi.fn().mockResolvedValue([]),
   },
 }));