fix: 为检查更新按钮添加加载状态

- 在更新管理 hook 中暴露检查更新中的 loading 状态
- 检查更新请求结束后统一复位 loading 状态
- 关于页检查更新按钮接入 loading 动画
- 补充测试覆盖检查中的 pending 状态

Fixes #730

frontend/src/App.tsx

@@ -2368,6 +2368,7 @@ function App() {
       hideUpdateDownloadProgress,
       isAboutOpen,
       isBackgroundProgressForLatestUpdate,
+      isCheckingForUpdates,
       isLatestUpdateDownloaded,
       isUpdateChannelLoading,
       isUpdateChannelSaving,
@@ -5162,7 +5163,14 @@ function App() {
       lastUpdateInfo?.hasUpdate && !isLatestUpdateDownloaded && !isBackgroundProgressForLatestUpdate ? (
           <Button key="mute" onClick={muteLatestUpdate}>{t('app.about.action.mute_this_version')}</Button>
       ) : null,
-      <Button key="check" icon={<CloudDownloadOutlined />} onClick={() => checkForUpdates(false)}>{t('app.about.action.check_updates')}</Button>,
+      <Button
+          key="check"
+          icon={<CloudDownloadOutlined />}
+          loading={isCheckingForUpdates}
+          onClick={() => checkForUpdates(false)}
+      >
+          {t('app.about.action.check_updates')}
+      </Button>,
       closeAction ?? null,
       lastUpdateInfo?.hasUpdate && !isLatestUpdateDownloaded && !isBackgroundProgressForLatestUpdate ? (
           <Button key="download" type="primary" icon={<DownloadOutlined />} onClick={() => downloadUpdate(lastUpdateInfo, false)}>{updateDownloadActionLabel}</Button>

frontend/src/hooks/useAppUpdateManager.test.tsx

@@ -198,6 +198,38 @@ describe('useAppUpdateManager', () => {
     expect(backendApp.CheckForUpdates).not.toHaveBeenCalled();
   });
 
+  it('exposes a loading state while checking for updates', async () => {
+    let resolveCheck: ((result: Record<string, unknown>) => void) | undefined;
+    const checkPromise = new Promise<Record<string, unknown>>((resolve) => {
+      resolveCheck = resolve;
+    });
+    backendApp.CheckForUpdates.mockReturnValue(checkPromise);
+
+    renderHook();
+
+    let pendingCheck: Promise<void> | undefined;
+    act(() => {
+      pendingCheck = hook?.checkForUpdates(false);
+    });
+
+    expect(hook?.isCheckingForUpdates).toBe(true);
+    expect(hook?.aboutUpdateStatus).toBe('app.about.update_status.checking');
+
+    await act(async () => {
+      resolveCheck?.({
+        success: true,
+        data: {
+          hasUpdate: false,
+          currentVersion: '0.8.1',
+          latestVersion: '0.8.1',
+        },
+      });
+      await pendingCheck;
+    });
+
+    expect(hook?.isCheckingForUpdates).toBe(false);
+  });
+
   it('merges complete MSI download metadata returned by the backend', async () => {
     backendApp.CheckForUpdates.mockResolvedValue({
       success: true,

frontend/src/hooks/useAppUpdateManager.ts

@@ -221,6 +221,7 @@ export const useAppUpdateManager = ({
   const [installMode, setInstallMode] = useState<UpdateInstallMode>('unknown');
   const [isUpdateChannelLoading, setIsUpdateChannelLoading] = useState(false);
   const [isUpdateChannelSaving, setIsUpdateChannelSaving] = useState(false);
+  const [isCheckingForUpdates, setIsCheckingForUpdates] = useState(false);
   const [aboutInfo, setAboutInfo] = useState<AboutInfo>(() => DEFAULT_ABOUT_INFO);
   const [aboutUpdateStatus, setAboutUpdateStatus] = useState<string>('');
   const [lastUpdateInfo, setLastUpdateInfo] = useState<UpdateInfo | null>(null);
@@ -470,6 +471,7 @@ export const useAppUpdateManager = ({
   const checkForUpdates = useCallback(async (silent: boolean) => {
     if (updateCheckInFlightRef.current) return;
     updateCheckInFlightRef.current = true;
+    setIsCheckingForUpdates(true);
     if (!silent) {
       setAboutUpdateStatus(t('app.about.update_status.checking'));
     }
@@ -477,8 +479,13 @@ export const useAppUpdateManager = ({
     const checkFn = silent && typeof updateAPI.CheckForUpdatesSilently === 'function'
       ? updateAPI.CheckForUpdatesSilently
       : updateAPI.CheckForUpdates;
-    const res = await checkFn();
-    updateCheckInFlightRef.current = false;
+    let res: any = null;
+    try {
+      res = await checkFn();
+    } finally {
+      updateCheckInFlightRef.current = false;
+      setIsCheckingForUpdates(false);
+    }
     if (!res?.success) {
       if (!silent) {
         const error = res?.message || t('common.unknown');
@@ -785,6 +792,7 @@ export const useAppUpdateManager = ({
     hideUpdateDownloadProgress,
     isAboutOpen,
     isBackgroundProgressForLatestUpdate,
+    isCheckingForUpdates,
     isLatestUpdateDownloaded,
     isUpdateChannelLoading,
     isUpdateChannelSaving,