fix(admin-web): 修复固定账户组件空值检查和 hooks 顺序

- 添加 data 空值检查防止 undefined 错误
- 将 useState hooks 移到条件返回之前（React hooks 规则）

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/admin-web/src/components/features/system-account-report/SystemAccountsTab.tsx

@@ -300,6 +300,16 @@ export default function SystemAccountsTab() {
  * [2026-01-07] 更新：添加查看分类账明细按钮，在卡片下方公共区域显示明细
  */
 function FixedAccountsSection({ data }: { data: SystemAccountReportResponse['fixedAccounts'] }) {
+  // [2026-01-07] 新增：选中账户和分类账数据（hooks 必须在条件返回之前）
+  const [selectedAccount, setSelectedAccount] = useState<string | null>(null);
+  const [allLedgerData, setAllLedgerData] = useState<AllSystemAccountsLedgerResponse | null>(null);
+  const [ledgerLoading, setLedgerLoading] = useState(false);
+
+  // [2026-01-07] 修复：添加空值检查，防止 data 为 undefined 时报错
+  if (!data) {
+    return <div className={styles.empty}>固定账户数据加载中...</div>;
+  }
+
   // [2026-01-07] 修复：从后端返回数据中读取真实的 accountSequence，过滤掉不存在的账户
   // 后端映射：S0000000001=HQ_COMMUNITY, S0000000002=COST_ACCOUNT, S0000000003=OPERATION_ACCOUNT
   const accounts = [
@@ -315,11 +325,6 @@ function FixedAccountsSection({ data }: { data: SystemAccountReportResponse['fix
       sequence: item.data?.accountSequence || '',
     }));
 
-  // [2026-01-07] 新增：选中账户和分类账数据
-  const [selectedAccount, setSelectedAccount] = useState<string | null>(null);
-  const [allLedgerData, setAllLedgerData] = useState<AllSystemAccountsLedgerResponse | null>(null);
-  const [ledgerLoading, setLedgerLoading] = useState(false);
-
   // 加载所有固定账户的分类账明细
   const loadAllLedger = useCallback(async () => {
     if (allLedgerData) return; // 已加载过，不重复加载